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 $13.25   3.842%   $13.7591   $13.76   $13.75   $13.80  
  Purchase #2 $176.91   6.826%   $188.9859   $188.99   $189.00   $189.00  
  Purchase #3 $13.37   11.188%   $14.8658   $14.87   $14.85   $14.90  
  Purchase #4 $163.46   6.143%   $173.5013   $173.50   $173.50   $173.50  
  Purchase #5 $84.50   11.334%   $94.0772   $94.08   $94.10   $94.10  
  Purchase #6 $89.33   13.808%   $101.6647   $101.66   $101.65   $101.70  
  Purchase #7 $24.74   10.619%   $27.3671   $27.37   $27.35   $27.40  
  7 purchase totals = $565.56       $614.2211   $614.23   $614.20   $614.40