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 $168.48   5.421%   $177.6133   $177.61   $177.60   $177.60  
  Purchase #2 $101.43   7.114%   $108.6457   $108.65   $108.65   $108.60  
  Purchase #3 $84.64   7.329%   $90.8433   $90.84   $90.85   $90.80  
  Purchase #4 $173.97   5.863%   $184.1699   $184.17   $184.15   $184.20  
  Purchase #5 $10.84   7.523%   $11.6555   $11.66   $11.65   $11.70  
  Purchase #6 $169.79   9.217%   $185.4395   $185.44   $185.45   $185.40  
  Purchase #7 $141.30   8.732%   $153.6383   $153.64   $153.65   $153.60  
  7 purchase totals = $850.45       $912.0055   $912.01   $912.00   $911.90