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 $194.43   3.360%   $200.9628   $200.96   $200.95   $201.00  
  Purchase #2 $62.69   11.123%   $69.663   $69.66   $69.65   $69.70  
  Purchase #3 $54.91   10.741%   $60.8079   $60.81   $60.80   $60.80  
  Purchase #4 $221.62   10.629%   $245.176   $245.18   $245.20   $245.20  
  Purchase #5 $106.47   10.722%   $117.8857   $117.89   $117.90   $117.90  
  Purchase #6 $38.54   10.563%   $42.611   $42.61   $42.60   $42.60  
  Purchase #7 $160.89   5.494%   $169.7293   $169.73   $169.75   $169.70  
  7 purchase totals = $839.55       $906.8357   $906.84   $906.85   $906.90