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 $53.65   11.857%   $60.0113   $60.01   $60.00   $60.00  
  Purchase #2 $161.98   13.573%   $183.9655   $183.97   $183.95   $184.00  
  Purchase #3 $156.89   13.318%   $177.7846   $177.78   $177.80   $177.80  
  Purchase #4 $114.56   8.150%   $123.8966   $123.90   $123.90   $123.90  
  Purchase #5 $16.94   12.302%   $19.024   $19.02   $19.00   $19.00  
  Purchase #6 $53.72   12.350%   $60.3544   $60.35   $60.35   $60.40  
  Purchase #7 $102.50   10.265%   $113.0216   $113.02   $113.00   $113.00  
  7 purchase totals = $660.24       $738.0580   $738.05   $738.00   $738.10