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 $85.55   11.766%   $95.6158   $95.62   $95.60   $95.60  
  Purchase #2 $23.26   6.624%   $24.8007   $24.80   $24.80   $24.80  
  Purchase #3 $233.83   6.398%   $248.7904   $248.79   $248.80   $248.80  
  Purchase #4 $103.93   8.304%   $112.5603   $112.56   $112.55   $112.60  
  Purchase #5 $202.79   6.461%   $215.8923   $215.89   $215.90   $215.90  
  Purchase #6 $95.63   9.528%   $104.7416   $104.74   $104.75   $104.70  
  Purchase #7 $219.55   4.149%   $228.6591   $228.66   $228.65   $228.70  
  7 purchase totals = $964.54       $1,031.0602   $1,031.06   $1,031.05   $1,031.10