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 $193.37   12.347%   $217.2454   $217.25   $217.25   $217.20  
  Purchase #2 $66.39   3.679%   $68.8325   $68.83   $68.85   $68.80  
  Purchase #3 $189.52   12.510%   $213.229   $213.23   $213.25   $213.20  
  Purchase #4 $67.58   10.750%   $74.8449   $74.84   $74.85   $74.80  
  Purchase #5 $68.62   11.153%   $76.2732   $76.27   $76.25   $76.30  
  Purchase #6 $45.27   8.327%   $49.0396   $49.04   $49.05   $49.00  
  Purchase #7 $241.42   10.398%   $266.5229   $266.52   $266.50   $266.50  
  7 purchase totals = $872.17       $965.9875   $965.98   $966.00   $965.80