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 $236.65   5.225%   $249.015   $249.02   $249.00   $249.00  
  Purchase #2 $173.46   9.157%   $189.3437   $189.34   $189.35   $189.30  
  Purchase #3 $115.58   9.563%   $126.6329   $126.63   $126.65   $126.60  
  Purchase #4 $144.31   11.443%   $160.8234   $160.82   $160.80   $160.80  
  Purchase #5 $171.36   4.565%   $179.1826   $179.18   $179.20   $179.20  
  Purchase #6 $17.53   8.692%   $19.0537   $19.05   $19.05   $19.10  
  Purchase #7 $97.40   11.108%   $108.2192   $108.22   $108.20   $108.20  
  7 purchase totals = $956.29       $1,032.2705   $1,032.26   $1,032.25   $1,032.20