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 $176.82   13.664%   $200.9807   $200.98   $201.00   $201.00  
  Purchase #2 $100.65   5.768%   $106.4555   $106.46   $106.45   $106.50  
  Purchase #3 $119.64   4.826%   $125.4138   $125.41   $125.40   $125.40  
  Purchase #4 $21.58   6.811%   $23.0498   $23.05   $23.05   $23.00  
  Purchase #5 $10.60   10.752%   $11.7397   $11.74   $11.75   $11.70  
  Purchase #6 $169.39   4.511%   $177.0312   $177.03   $177.05   $177.00  
  Purchase #7 $76.29   11.127%   $84.7788   $84.78   $84.80   $84.80  
  7 purchase totals = $674.97       $729.4495   $729.45   $729.50   $729.40