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 $199.54   9.234%   $217.9655   $217.97   $217.95   $218.00  
  Purchase #2 $102.93   3.127%   $106.1486   $106.15   $106.15   $106.10  
  Purchase #3 $65.70   7.861%   $70.8647   $70.86   $70.85   $70.90  
  Purchase #4 $73.62   7.645%   $79.2482   $79.25   $79.25   $79.20  
  Purchase #5 $5.30   10.724%   $5.8684   $5.87   $5.85   $5.90  
  Purchase #6 $176.92   11.725%   $197.6639   $197.66   $197.65   $197.70  
  Purchase #7 $68.38   10.728%   $75.7158   $75.72   $75.70   $75.70  
  7 purchase totals = $692.39       $753.4751   $753.48   $753.40   $753.50