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	$165.61	7.303%	$177.7045	$177.70	$177.70	$177.70
Purchase #2	$18.27	12.505%	$20.5547	$20.55	$20.55	$20.60
Purchase #3	$132.55	10.775%	$146.8323	$146.83	$146.85	$146.80
Purchase #4	$94.34	5.859%	$99.8674	$99.87	$99.85	$99.90
Purchase #5	$165.31	6.180%	$175.5262	$175.53	$175.55	$175.50
Purchase #6	$85.77	6.696%	$91.5132	$91.51	$91.50	$91.50
Purchase #7	$182.57	3.265%	$188.5309	$188.53	$188.55	$188.50
7 purchase totals =	$844.42		$900.5292	$900.52	$900.55	$900.50