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 $62.39   6.155%   $66.2301   $66.23   $66.25   $66.20  
  Purchase #2 $163.86   9.616%   $179.6168   $179.62   $179.60   $179.60  
  Purchase #3 $134.26   8.272%   $145.366   $145.37   $145.35   $145.40  
  Purchase #4 $108.66   7.190%   $116.4727   $116.47   $116.45   $116.50  
  Purchase #5 $52.35   5.397%   $55.1753   $55.18   $55.20   $55.20  
  Purchase #6 $163.83   8.302%   $177.4312   $177.43   $177.45   $177.40  
  Purchase #7 $169.99   9.130%   $185.5101   $185.51   $185.50   $185.50  
  7 purchase totals = $855.34       $925.8022   $925.81   $925.80   $925.80