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 $84.83   9.870%   $93.2027   $93.20   $93.20   $93.20  
  Purchase #2 $59.39   5.796%   $62.8322   $62.83   $62.85   $62.80  
  Purchase #3 $57.52   9.742%   $63.1236   $63.12   $63.10   $63.10  
  Purchase #4 $10.29   10.236%   $11.3433   $11.34   $11.35   $11.30  
  Purchase #5 $126.82   5.537%   $133.842   $133.84   $133.85   $133.80  
  Purchase #6 $119.37   8.841%   $129.9235   $129.92   $129.90   $129.90  
  Purchase #7 $7.93   10.299%   $8.7467   $8.75   $8.75   $8.70  
  7 purchase totals = $466.15       $503.0140   $503.00   $503.00   $502.80