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 $236.76   7.762%   $255.1373   $255.14   $255.15   $255.10  
  Purchase #2 $22.47   9.230%   $24.544   $24.54   $24.55   $24.50  
  Purchase #3 $151.77   7.173%   $162.6565   $162.66   $162.65   $162.70  
  Purchase #4 $246.86   12.850%   $278.5815   $278.58   $278.60   $278.60  
  Purchase #5 $114.42   13.145%   $129.4605   $129.46   $129.45   $129.50  
  Purchase #6 $250.55   10.580%   $277.0582   $277.06   $277.05   $277.10  
  Purchase #7 $206.43   4.696%   $216.124   $216.12   $216.10   $216.10  
  7 purchase totals = $1,229.26       $1,343.5620   $1,343.56   $1,343.55   $1,343.60