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 $197.69   3.666%   $204.9373   $204.94   $204.95   $204.90  
  Purchase #2 $116.76   4.836%   $122.4065   $122.41   $122.40   $122.40  
  Purchase #3 $68.57   12.282%   $76.9918   $76.99   $77.00   $77.00  
  Purchase #4 $58.88   13.391%   $66.7646   $66.76   $66.75   $66.80  
  Purchase #5 $88.63   6.264%   $94.1818   $94.18   $94.20   $94.20  
  Purchase #6 $210.99   6.164%   $223.9954   $224.00   $224.00   $224.00  
  Purchase #7 $152.88   13.802%   $173.9805   $173.98   $174.00   $174.00  
  7 purchase totals = $894.40       $963.2579   $963.26   $963.30   $963.30