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 $46.33   13.566%   $52.6151   $52.62   $52.60   $52.60  
  Purchase #2 $115.96   9.274%   $126.7141   $126.71   $126.70   $126.70  
  Purchase #3 $36.75   8.550%   $39.8921   $39.89   $39.90   $39.90  
  Purchase #4 $77.43   10.169%   $85.3039   $85.30   $85.30   $85.30  
  Purchase #5 $166.59   9.350%   $182.1662   $182.17   $182.15   $182.20  
  Purchase #6 $139.54   5.282%   $146.9105   $146.91   $146.90   $146.90  
  Purchase #7 $131.58   9.717%   $144.3656   $144.37   $144.35   $144.40  
  7 purchase totals = $714.18       $777.9675   $777.97   $777.90   $778.00