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 $8.92   13.496%   $10.1238   $10.12   $10.10   $10.10  
  Purchase #2 $245.91   4.472%   $256.9071   $256.91   $256.90   $256.90  
  Purchase #3 $62.79   3.393%   $64.9205   $64.92   $64.90   $64.90  
  Purchase #4 $99.46   5.279%   $104.7105   $104.71   $104.70   $104.70  
  Purchase #5 $115.73   11.564%   $129.113   $129.11   $129.10   $129.10  
  Purchase #6 $156.62   6.260%   $166.4244   $166.42   $166.40   $166.40  
  Purchase #7 $38.35   6.768%   $40.9455   $40.95   $40.95   $40.90  
  7 purchase totals = $727.78       $773.1448   $773.14   $773.05   $773.00