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 $206.67   9.248%   $225.7828   $225.78   $225.80   $225.80  
  Purchase #2 $135.60   13.788%   $154.2965   $154.30   $154.30   $154.30  
  Purchase #3 $56.33   6.691%   $60.099   $60.10   $60.10   $60.10  
  Purchase #4 $75.44   10.870%   $83.6403   $83.64   $83.65   $83.60  
  Purchase #5 $174.48   4.458%   $182.2583   $182.26   $182.25   $182.30  
  Purchase #6 $169.79   12.604%   $191.1903   $191.19   $191.20   $191.20  
  Purchase #7 $46.63   5.763%   $49.3173   $49.32   $49.30   $49.30  
  7 purchase totals = $864.94       $946.5845   $946.59   $946.60   $946.60