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 $85.39   12.437%   $96.01   $96.01   $96.00   $96.00  
  Purchase #2 $161.57   8.250%   $174.8995   $174.90   $174.90   $174.90  
  Purchase #3 $31.74   12.555%   $35.725   $35.73   $35.75   $35.70  
  Purchase #4 $91.85   8.645%   $99.7904   $99.79   $99.80   $99.80  
  Purchase #5 $126.75   10.684%   $140.292   $140.29   $140.30   $140.30  
  Purchase #6 $110.72   8.654%   $120.3017   $120.30   $120.30   $120.30  
  Purchase #7 $168.36   8.262%   $182.2699   $182.27   $182.25   $182.30  
  7 purchase totals = $776.38       $849.2885   $849.29   $849.30   $849.30