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 $119.45   4.423%   $124.7333   $124.73   $124.75   $124.70  
  Purchase #2 $180.68   12.671%   $203.574   $203.57   $203.55   $203.60  
  Purchase #3 $208.93   12.233%   $234.4884   $234.49   $234.50   $234.50  
  Purchase #4 $132.38   11.706%   $147.8764   $147.88   $147.90   $147.90  
  Purchase #5 $9.78   11.130%   $10.8685   $10.87   $10.85   $10.90  
  Purchase #6 $106.88   11.280%   $118.9361   $118.94   $118.95   $118.90  
  Purchase #7 $166.55   6.123%   $176.7479   $176.75   $176.75   $176.70  
  7 purchase totals = $924.65       $1,017.2246   $1,017.23   $1,017.25   $1,017.20