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 $180.53   8.323%   $195.5555   $195.56   $195.55   $195.60  
  Purchase #2 $121.97   3.362%   $126.0706   $126.07   $126.05   $126.10  
  Purchase #3 $211.35   8.817%   $229.9847   $229.98   $230.00   $230.00  
  Purchase #4 $91.97   6.193%   $97.6657   $97.67   $97.65   $97.70  
  Purchase #5 $207.41   9.683%   $227.4935   $227.49   $227.50   $227.50  
  Purchase #6 $162.43   7.405%   $174.4579   $174.46   $174.45   $174.50  
  Purchase #7 $236.68   13.841%   $269.4389   $269.44   $269.45   $269.40  
  7 purchase totals = $1,212.34       $1,320.6668   $1,320.67   $1,320.65   $1,320.80