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 $249.34   7.855%   $268.9257   $268.93   $268.95   $268.90  
  Purchase #2 $216.93   12.753%   $244.5951   $244.60   $244.60   $244.60  
  Purchase #3 $133.98   11.698%   $149.653   $149.65   $149.65   $149.70  
  Purchase #4 $8.97   6.706%   $9.5715   $9.57   $9.55   $9.60  
  Purchase #5 $23.71   6.778%   $25.3171   $25.32   $25.30   $25.30  
  Purchase #6 $229.97   8.801%   $250.2097   $250.21   $250.20   $250.20  
  Purchase #7 $78.62   9.827%   $86.346   $86.35   $86.35   $86.30  
  7 purchase totals = $941.52       $1,034.6181   $1,034.63   $1,034.60   $1,034.60