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 $41.97   13.480%   $47.6276   $47.63   $47.65   $47.60  
  Purchase #2 $229.32   13.758%   $260.8698   $260.87   $260.85   $260.90  
  Purchase #3 $184.55   10.773%   $204.4316   $204.43   $204.45   $204.40  
  Purchase #4 $17.35   9.347%   $18.9717   $18.97   $18.95   $19.00  
  Purchase #5 $193.85   8.424%   $210.1799   $210.18   $210.20   $210.20  
  Purchase #6 $245.59   3.378%   $253.886   $253.89   $253.90   $253.90  
  Purchase #7 $24.73   6.202%   $26.2638   $26.26   $26.25   $26.30  
  7 purchase totals = $937.36       $1,022.2304   $1,022.23   $1,022.25   $1,022.30