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 $110.94   6.526%   $118.1799   $118.18   $118.20   $118.20  
  Purchase #2 $77.92   7.245%   $83.5653   $83.57   $83.55   $83.60  
  Purchase #3 $79.43   9.324%   $86.8361   $86.84   $86.85   $86.80  
  Purchase #4 $162.98   8.550%   $176.9148   $176.91   $176.90   $176.90  
  Purchase #5 $93.32   4.284%   $97.3178   $97.32   $97.30   $97.30  
  Purchase #6 $13.53   4.694%   $14.1651   $14.17   $14.15   $14.20  
  Purchase #7 $68.87   12.190%   $77.2653   $77.27   $77.25   $77.30  
  7 purchase totals = $606.99       $654.2443   $654.26   $654.20   $654.30