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	$67.93	5.138%	$71.4202	$71.42	$71.40	$71.40
Purchase #2	$127.32	10.606%	$140.8236	$140.82	$140.80	$140.80
Purchase #3	$248.84	12.249%	$279.3204	$279.32	$279.30	$279.30
Purchase #4	$59.48	9.263%	$64.9896	$64.99	$65.00	$65.00
Purchase #5	$200.57	4.662%	$209.9206	$209.92	$209.90	$209.90
Purchase #6	$167.63	12.656%	$188.8453	$188.85	$188.85	$188.80
Purchase #7	$34.87	10.799%	$38.6356	$38.64	$38.65	$38.60
7 purchase totals =	$906.64		$993.9553	$993.96	$993.90	$993.80