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 $32.83   3.716%   $34.05   $34.05   $34.05   $34.10  
  Purchase #2 $239.55   4.542%   $250.4304   $250.43   $250.45   $250.40  
  Purchase #3 $57.46   11.455%   $64.042   $64.04   $64.05   $64.00  
  Purchase #4 $58.82   6.823%   $62.8333   $62.83   $62.85   $62.80  
  Purchase #5 $114.82   9.742%   $126.0058   $126.01   $126.00   $126.00  
  Purchase #6 $171.55   11.848%   $191.8752   $191.88   $191.90   $191.90  
  Purchase #7 $201.60   3.653%   $208.9644   $208.96   $208.95   $209.00  
  7 purchase totals = $876.63       $938.2011   $938.20   $938.25   $938.20