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 $44.74   5.820%   $47.3439   $47.34   $47.35   $47.30  
  Purchase #2 $116.87   6.640%   $124.6302   $124.63   $124.65   $124.60  
  Purchase #3 $193.56   3.182%   $199.7191   $199.72   $199.70   $199.70  
  Purchase #4 $96.82   12.165%   $108.5982   $108.60   $108.60   $108.60  
  Purchase #5 $8.92   11.211%   $9.92   $9.92   $9.90   $9.90  
  Purchase #6 $238.51   8.732%   $259.3367   $259.34   $259.35   $259.30  
  Purchase #7 $80.76   9.414%   $88.3627   $88.36   $88.35   $88.40  
  7 purchase totals = $780.18       $837.9108   $837.91   $837.90   $837.80