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 $105.44   13.550%   $119.7271   $119.73   $119.75   $119.70  
  Purchase #2 $93.27   11.220%   $103.7349   $103.73   $103.75   $103.70  
  Purchase #3 $36.32   8.324%   $39.3433   $39.34   $39.35   $39.30  
  Purchase #4 $30.29   3.674%   $31.4029   $31.40   $31.40   $31.40  
  Purchase #5 $119.85   3.620%   $124.1886   $124.19   $124.20   $124.20  
  Purchase #6 $212.86   8.112%   $230.1272   $230.13   $230.15   $230.10  
  Purchase #7 $139.93   9.485%   $153.2024   $153.20   $153.20   $153.20  
  7 purchase totals = $737.96       $801.7264   $801.72   $801.80   $801.60