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 $69.52   13.204%   $78.6994   $78.70   $78.70   $78.70  
  Purchase #2 $50.67   9.135%   $55.2987   $55.30   $55.30   $55.30  
  Purchase #3 $94.25   3.802%   $97.8334   $97.83   $97.85   $97.80  
  Purchase #4 $23.95   6.136%   $25.4196   $25.42   $25.40   $25.40  
  Purchase #5 $208.72   5.591%   $220.3895   $220.39   $220.40   $220.40  
  Purchase #6 $220.99   9.686%   $242.3951   $242.40   $242.40   $242.40  
  Purchase #7 $14.78   4.543%   $15.4515   $15.45   $15.45   $15.50  
  7 purchase totals = $682.88       $735.4872   $735.49   $735.50   $735.50