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 $62.44   13.611%   $70.9387   $70.94   $70.95   $70.90  
  Purchase #2 $82.90   4.785%   $86.8668   $86.87   $86.85   $86.90  
  Purchase #3 $177.52   13.352%   $201.2225   $201.22   $201.20   $201.20  
  Purchase #4 $60.63   13.440%   $68.7787   $68.78   $68.80   $68.80  
  Purchase #5 $44.36   9.340%   $48.5032   $48.50   $48.50   $48.50  
  Purchase #6 $239.37   12.104%   $268.3433   $268.34   $268.35   $268.30  
  Purchase #7 $11.47   8.378%   $12.431   $12.43   $12.45   $12.40  
  7 purchase totals = $678.69       $757.0842   $757.08   $757.10   $757.00