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 $42.62   3.203%   $43.9851   $43.99   $44.00   $44.00  
  Purchase #2 $104.71   13.585%   $118.9349   $118.93   $118.95   $118.90  
  Purchase #3 $201.76   10.190%   $222.3193   $222.32   $222.30   $222.30  
  Purchase #4 $173.62   8.351%   $188.119   $188.12   $188.10   $188.10  
  Purchase #5 $152.76   12.185%   $171.3738   $171.37   $171.35   $171.40  
  Purchase #6 $139.85   3.137%   $144.2371   $144.24   $144.25   $144.20  
  Purchase #7 $71.40   8.788%   $77.6746   $77.67   $77.65   $77.70  
  7 purchase totals = $886.72       $966.6438   $966.64   $966.60   $966.60