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 $32.67   5.124%   $34.344   $34.34   $34.35   $34.30  
  Purchase #2 $104.94   4.543%   $109.7074   $109.71   $109.70   $109.70  
  Purchase #3 $207.37   5.592%   $218.9661   $218.97   $218.95   $219.00  
  Purchase #4 $236.81   4.814%   $248.21   $248.21   $248.20   $248.20  
  Purchase #5 $85.78   10.742%   $94.9945   $94.99   $95.00   $95.00  
  Purchase #6 $43.27   6.860%   $46.2383   $46.24   $46.25   $46.20  
  Purchase #7 $214.94   11.161%   $238.9295   $238.93   $238.95   $238.90  
  7 purchase totals = $925.78       $991.3898   $991.39   $991.40   $991.30