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 $67.25   13.290%   $76.1875   $76.19   $76.20   $76.20  
  Purchase #2 $14.59   4.763%   $15.2849   $15.28   $15.30   $15.30  
  Purchase #3 $213.75   5.809%   $226.1667   $226.17   $226.15   $226.20  
  Purchase #4 $239.46   12.438%   $269.244   $269.24   $269.25   $269.20  
  Purchase #5 $12.92   3.379%   $13.3566   $13.36   $13.35   $13.40  
  Purchase #6 $110.64   4.859%   $116.016   $116.02   $116.00   $116.00  
  Purchase #7 $110.25   7.745%   $118.7889   $118.79   $118.80   $118.80  
  7 purchase totals = $768.86       $835.0446   $835.05   $835.05   $835.10