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 $246.84   9.493%   $270.2725   $270.27   $270.25   $270.30  
  Purchase #2 $86.30   9.738%   $94.7039   $94.70   $94.70   $94.70  
  Purchase #3 $69.90   8.145%   $75.5934   $75.59   $75.60   $75.60  
  Purchase #4 $173.44   5.571%   $183.1023   $183.10   $183.10   $183.10  
  Purchase #5 $7.85   10.449%   $8.6702   $8.67   $8.65   $8.70  
  Purchase #6 $199.49   12.756%   $224.9369   $224.94   $224.95   $224.90  
  Purchase #7 $171.92   13.428%   $195.0054   $195.01   $195.00   $195.00  
  7 purchase totals = $955.74       $1,052.2846   $1,052.28   $1,052.25   $1,052.30