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 $182.86   6.800%   $195.2945   $195.29   $195.30   $195.30  
  Purchase #2 $84.35   6.502%   $89.8344   $89.83   $89.85   $89.80  
  Purchase #3 $107.80   3.227%   $111.2787   $111.28   $111.30   $111.30  
  Purchase #4 $69.72   8.508%   $75.6518   $75.65   $75.65   $75.70  
  Purchase #5 $50.63   3.435%   $52.3691   $52.37   $52.35   $52.40  
  Purchase #6 $216.50   11.336%   $241.0424   $241.04   $241.05   $241.00  
  Purchase #7 $36.27   8.367%   $39.3047   $39.30   $39.30   $39.30  
  7 purchase totals = $748.13       $804.7756   $804.76   $804.80   $804.80