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 $69.35   8.121%   $74.9819   $74.98   $75.00   $75.00  
  Purchase #2 $149.90   6.156%   $159.1278   $159.13   $159.15   $159.10  
  Purchase #3 $165.69   4.228%   $172.6954   $172.70   $172.70   $172.70  
  Purchase #4 $79.39   4.431%   $82.9078   $82.91   $82.90   $82.90  
  Purchase #5 $76.42   3.404%   $79.0213   $79.02   $79.00   $79.00  
  Purchase #6 $116.87   4.421%   $122.0368   $122.04   $122.05   $122.00  
  Purchase #7 $220.71   10.633%   $244.1781   $244.18   $244.20   $244.20  
  7 purchase totals = $878.33       $934.9491   $934.96   $935.00   $934.90