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 $50.72   11.134%   $56.3672   $56.37   $56.35   $56.40  
  Purchase #2 $121.41   7.582%   $130.6153   $130.62   $130.60   $130.60  
  Purchase #3 $192.42   5.755%   $203.4938   $203.49   $203.50   $203.50  
  Purchase #4 $14.75   13.617%   $16.7585   $16.76   $16.75   $16.80  
  Purchase #5 $228.97   3.414%   $236.787   $236.79   $236.80   $236.80  
  Purchase #6 $94.48   5.518%   $99.6934   $99.69   $99.70   $99.70  
  Purchase #7 $187.67   7.108%   $201.0096   $201.01   $201.00   $201.00  
  7 purchase totals = $890.42       $944.7248   $944.73   $944.70   $944.80