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 $83.51   12.518%   $93.9638   $93.96   $93.95   $94.00  
  Purchase #2 $109.78   10.598%   $121.4145   $121.41   $121.40   $121.40  
  Purchase #3 $131.50   3.593%   $136.2248   $136.22   $136.20   $136.20  
  Purchase #4 $227.27   12.196%   $254.9878   $254.99   $255.00   $255.00  
  Purchase #5 $77.41   8.171%   $83.7352   $83.74   $83.75   $83.70  
  Purchase #6 $90.55   5.577%   $95.6   $95.60   $95.60   $95.60  
  Purchase #7 $234.84   11.204%   $261.1515   $261.15   $261.15   $261.20  
  7 purchase totals = $954.86       $1,047.0776   $1,047.07   $1,047.05   $1,047.10