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 $191.34   6.696%   $204.1521   $204.15   $204.15   $204.20  
  Purchase #2 $111.50   7.434%   $119.7889   $119.79   $119.80   $119.80  
  Purchase #3 $145.27   9.797%   $159.5021   $159.50   $159.50   $159.50  
  Purchase #4 $133.28   12.515%   $149.96   $149.96   $149.95   $150.00  
  Purchase #5 $225.26   8.672%   $244.7945   $244.79   $244.80   $244.80  
  Purchase #6 $67.34   13.703%   $76.5676   $76.57   $76.55   $76.60  
  Purchase #7 $60.41   6.403%   $64.2781   $64.28   $64.30   $64.30  
  7 purchase totals = $934.40       $1,019.0433   $1,019.04   $1,019.05   $1,019.20