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 $225.56   7.172%   $241.7372   $241.74   $241.75   $241.70  
  Purchase #2 $213.82   13.794%   $243.3143   $243.31   $243.30   $243.30  
  Purchase #3 $204.47   5.682%   $216.088   $216.09   $216.10   $216.10  
  Purchase #4 $171.81   11.154%   $190.9737   $190.97   $190.95   $191.00  
  Purchase #5 $94.83   3.699%   $98.3378   $98.34   $98.35   $98.30  
  Purchase #6 $20.76   11.314%   $23.1088   $23.11   $23.10   $23.10  
  Purchase #7 $21.84   3.262%   $22.5524   $22.55   $22.55   $22.60  
  7 purchase totals = $953.09       $1,036.1122   $1,036.11   $1,036.10   $1,036.10