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 $84.41   12.704%   $95.1334   $95.13   $95.15   $95.10  
  Purchase #2 $237.62   6.686%   $253.5073   $253.51   $253.50   $253.50  
  Purchase #3 $44.77   8.736%   $48.6811   $48.68   $48.70   $48.70  
  Purchase #4 $170.49   13.199%   $192.993   $192.99   $193.00   $193.00  
  Purchase #5 $223.89   9.321%   $244.7588   $244.76   $244.75   $244.80  
  Purchase #6 $20.39   12.534%   $22.9457   $22.95   $22.95   $22.90  
  Purchase #7 $126.62   13.836%   $144.1391   $144.14   $144.15   $144.10  
  7 purchase totals = $908.19       $1,002.1584   $1,002.16   $1,002.20   $1,002.10