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 $32.74   11.306%   $36.4416   $36.44   $36.45   $36.40  
  Purchase #2 $62.54   6.329%   $66.4982   $66.50   $66.50   $66.50  
  Purchase #3 $250.64   12.235%   $281.3058   $281.31   $281.30   $281.30  
  Purchase #4 $121.62   13.694%   $138.2746   $138.27   $138.25   $138.30  
  Purchase #5 $170.86   10.636%   $189.0327   $189.03   $189.05   $189.00  
  Purchase #6 $104.55   5.134%   $109.9176   $109.92   $109.90   $109.90  
  Purchase #7 $183.63   9.473%   $201.0253   $201.03   $201.05   $201.00  
  7 purchase totals = $926.58       $1,022.4958   $1,022.50   $1,022.50   $1,022.40