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 $210.78   6.610%   $224.7126   $224.71   $224.70   $224.70  
  Purchase #2 $6.75   12.812%   $7.6148   $7.61   $7.60   $7.60  
  Purchase #3 $192.29   10.644%   $212.7573   $212.76   $212.75   $212.80  
  Purchase #4 $43.48   6.388%   $46.2575   $46.26   $46.25   $46.30  
  Purchase #5 $199.51   4.712%   $208.9109   $208.91   $208.90   $208.90  
  Purchase #6 $228.26   9.804%   $250.6386   $250.64   $250.65   $250.60  
  Purchase #7 $195.28   10.635%   $216.048   $216.05   $216.05   $216.00  
  7 purchase totals = $1,076.35       $1,166.9397   $1,166.94   $1,166.90   $1,166.90