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 $216.51   13.698%   $246.1675   $246.17   $246.15   $246.20  
  Purchase #2 $115.89   13.263%   $131.2605   $131.26   $131.25   $131.30  
  Purchase #3 $35.35   11.407%   $39.3824   $39.38   $39.40   $39.40  
  Purchase #4 $232.50   11.197%   $258.533   $258.53   $258.55   $258.50  
  Purchase #5 $212.35   6.661%   $226.4946   $226.49   $226.50   $226.50  
  Purchase #6 $62.28   3.221%   $64.286   $64.29   $64.30   $64.30  
  Purchase #7 $90.62   7.236%   $97.1773   $97.18   $97.20   $97.20  
  7 purchase totals = $965.50       $1,063.3013   $1,063.30   $1,063.35   $1,063.40