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 $14.49   11.829%   $16.204   $16.20   $16.20   $16.20  
  Purchase #2 $54.47   7.462%   $58.5346   $58.53   $58.55   $58.50  
  Purchase #3 $155.69   11.482%   $173.5663   $173.57   $173.55   $173.60  
  Purchase #4 $184.90   4.576%   $193.361   $193.36   $193.35   $193.40  
  Purchase #5 $104.95   11.128%   $116.6288   $116.63   $116.65   $116.60  
  Purchase #6 $117.40   12.631%   $132.2288   $132.23   $132.25   $132.20  
  Purchase #7 $159.28   3.603%   $165.0189   $165.02   $165.00   $165.00  
  7 purchase totals = $791.18       $855.5424   $855.54   $855.55   $855.50