Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $190.29   6.461%   $202.5846   $202.58   $202.60   $202.60  
  Purchase #2 $225.74   13.561%   $256.3526   $256.35   $256.35   $256.40  
  Purchase #3 $130.62   13.795%   $148.639   $148.64   $148.65   $148.60  
  Purchase #4 $243.55   13.684%   $276.8774   $276.88   $276.90   $276.90  
  Purchase #5 $105.77   12.551%   $119.0452   $119.05   $119.05   $119.00  
  Purchase #6 $215.69   4.605%   $225.6225   $225.62   $225.60   $225.60  
  Purchase #7 $194.34   11.387%   $216.4695   $216.47   $216.45   $216.50  
  7 purchase totals = $1,306.00       $1,445.5908   $1,445.59   $1,445.60   $1,445.60