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 $56.45   6.697%   $60.2305   $60.23   $60.25   $60.20  
  Purchase #2 $74.34   13.565%   $84.4242   $84.42   $84.40   $84.40  
  Purchase #3 $126.93   4.138%   $132.1824   $132.18   $132.20   $132.20  
  Purchase #4 $161.27   4.769%   $168.961   $168.96   $168.95   $169.00  
  Purchase #5 $62.47   5.446%   $65.8721   $65.87   $65.85   $65.90  
  Purchase #6 $241.67   5.851%   $255.8101   $255.81   $255.80   $255.80  
  Purchase #7 $177.88   7.558%   $191.3242   $191.32   $191.30   $191.30  
  7 purchase totals = $901.01       $958.8045   $958.79   $958.75   $958.80