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 $200.93   11.860%   $224.7603   $224.76   $224.75   $224.80  
  Purchase #2 $45.77   10.200%   $50.4385   $50.44   $50.45   $50.40  
  Purchase #3 $132.79   11.452%   $147.9971   $148.00   $148.00   $148.00  
  Purchase #4 $9.65   6.767%   $10.303   $10.30   $10.30   $10.30  
  Purchase #5 $119.49   12.651%   $134.6067   $134.61   $134.60   $134.60  
  Purchase #6 $170.66   3.656%   $176.8993   $176.90   $176.90   $176.90  
  Purchase #7 $191.61   9.720%   $210.2345   $210.23   $210.25   $210.20  
  7 purchase totals = $870.90       $955.2394   $955.24   $955.25   $955.20