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 $67.36   13.825%   $76.6725   $76.67   $76.65   $76.70  
  Purchase #2 $55.60   10.339%   $61.3485   $61.35   $61.35   $61.30  
  Purchase #3 $50.88   4.128%   $52.9803   $52.98   $53.00   $53.00  
  Purchase #4 $97.65   6.827%   $104.3166   $104.32   $104.30   $104.30  
  Purchase #5 $157.58   11.663%   $175.9586   $175.96   $175.95   $176.00  
  Purchase #6 $125.46   9.300%   $137.1278   $137.13   $137.15   $137.10  
  Purchase #7 $33.62   10.714%   $37.222   $37.22   $37.20   $37.20  
  7 purchase totals = $588.15       $645.6263   $645.63   $645.60   $645.60