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 $68.36   11.642%   $76.3185   $76.32   $76.30   $76.30  
  Purchase #2 $79.71   9.562%   $87.3319   $87.33   $87.35   $87.30  
  Purchase #3 $54.86   7.494%   $58.9712   $58.97   $58.95   $59.00  
  Purchase #4 $69.72   9.257%   $76.174   $76.17   $76.15   $76.20  
  Purchase #5 $211.76   4.381%   $221.0372   $221.04   $221.05   $221.00  
  Purchase #6 $64.30   4.638%   $67.2822   $67.28   $67.30   $67.30  
  Purchase #7 $159.80   6.586%   $170.3244   $170.32   $170.30   $170.30  
  7 purchase totals = $708.51       $757.4394   $757.43   $757.40   $757.40