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 $206.43   10.130%   $227.3414   $227.34   $227.35   $227.30  
  Purchase #2 $57.87   13.341%   $65.5904   $65.59   $65.60   $65.60  
  Purchase #3 $150.51   13.276%   $170.4917   $170.49   $170.50   $170.50  
  Purchase #4 $108.65   3.666%   $112.6331   $112.63   $112.65   $112.60  
  Purchase #5 $15.31   6.287%   $16.2725   $16.27   $16.25   $16.30  
  Purchase #6 $181.58   3.544%   $188.0152   $188.02   $188.00   $188.00  
  Purchase #7 $120.77   4.287%   $125.9474   $125.95   $125.95   $125.90  
  7 purchase totals = $841.12       $906.2917   $906.29   $906.30   $906.20