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 $207.92   11.733%   $232.3153   $232.32   $232.30   $232.30  
  Purchase #2 $85.37   10.314%   $94.1751   $94.18   $94.20   $94.20  
  Purchase #3 $118.63   10.707%   $131.3317   $131.33   $131.35   $131.30  
  Purchase #4 $61.52   6.297%   $65.3939   $65.39   $65.40   $65.40  
  Purchase #5 $13.81   11.824%   $15.4429   $15.44   $15.45   $15.40  
  Purchase #6 $24.63   11.256%   $27.4024   $27.40   $27.40   $27.40  
  Purchase #7 $36.87   5.783%   $39.0022   $39.00   $39.00   $39.00  
  7 purchase totals = $548.75       $605.0635   $605.06   $605.10   $605.00