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 $196.43   3.307%   $202.9259   $202.93   $202.95   $202.90  
  Purchase #2 $55.63   8.501%   $60.3591   $60.36   $60.35   $60.40  
  Purchase #3 $195.37   11.165%   $217.1831   $217.18   $217.20   $217.20  
  Purchase #4 $199.33   10.849%   $220.9553   $220.96   $220.95   $221.00  
  Purchase #5 $14.64   8.402%   $15.8701   $15.87   $15.85   $15.90  
  Purchase #6 $156.59   7.152%   $167.7893   $167.79   $167.80   $167.80  
  Purchase #7 $74.50   10.304%   $82.1765   $82.18   $82.20   $82.20  
  7 purchase totals = $892.49       $967.2593   $967.27   $967.30   $967.40