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 $68.28   10.335%   $75.3367   $75.34   $75.35   $75.30  
  Purchase #2 $148.29   8.523%   $160.9288   $160.93   $160.95   $160.90  
  Purchase #3 $39.76   9.231%   $43.4302   $43.43   $43.45   $43.40  
  Purchase #4 $205.83   9.543%   $225.4724   $225.47   $225.45   $225.50  
  Purchase #5 $121.42   11.491%   $135.3724   $135.37   $135.35   $135.40  
  Purchase #6 $16.35   10.483%   $18.064   $18.06   $18.05   $18.10  
  Purchase #7 $183.46   9.391%   $200.6887   $200.69   $200.70   $200.70  
  7 purchase totals = $783.39       $859.2932   $859.29   $859.30   $859.30