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 $58.32   6.256%   $61.9685   $61.97   $61.95   $62.00  
  Purchase #2 $166.36   8.305%   $180.1762   $180.18   $180.20   $180.20  
  Purchase #3 $119.74   8.165%   $129.5168   $129.52   $129.50   $129.50  
  Purchase #4 $204.31   13.246%   $231.3729   $231.37   $231.35   $231.40  
  Purchase #5 $138.88   4.249%   $144.781   $144.78   $144.80   $144.80  
  Purchase #6 $27.35   3.577%   $28.3283   $28.33   $28.35   $28.30  
  Purchase #7 $25.86   12.737%   $29.1538   $29.15   $29.15   $29.20  
  7 purchase totals = $740.82       $805.2975   $805.30   $805.30   $805.40