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 $64.38   7.654%   $69.3076   $69.31   $69.30   $69.30  
  Purchase #2 $55.67   12.417%   $62.5825   $62.58   $62.60   $62.60  
  Purchase #3 $25.91   5.743%   $27.398   $27.40   $27.40   $27.40  
  Purchase #4 $172.39   11.360%   $191.9735   $191.97   $191.95   $192.00  
  Purchase #5 $205.96   7.860%   $222.1485   $222.15   $222.15   $222.10  
  Purchase #6 $132.53   6.370%   $140.9722   $140.97   $140.95   $141.00  
  Purchase #7 $100.98   4.114%   $105.1343   $105.13   $105.15   $105.10  
  7 purchase totals = $757.82       $819.5166   $819.51   $819.50   $819.50