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 $30.46   8.216%   $32.9626   $32.96   $32.95   $33.00  
  Purchase #2 $200.51   8.789%   $218.1328   $218.13   $218.15   $218.10  
  Purchase #3 $165.81   5.508%   $174.9428   $174.94   $174.95   $174.90  
  Purchase #4 $235.37   8.164%   $254.5856   $254.59   $254.60   $254.60  
  Purchase #5 $222.33   10.420%   $245.4968   $245.50   $245.50   $245.50  
  Purchase #6 $156.43   7.758%   $168.5658   $168.57   $168.55   $168.60  
  Purchase #7 $140.73   8.856%   $153.193   $153.19   $153.20   $153.20  
  7 purchase totals = $1,151.64       $1,247.8794   $1,247.88   $1,247.90   $1,247.90