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	$89.41	11.499%	$99.6913	$99.69	$99.70	$99.70
Purchase #2	$209.72	7.242%	$224.9079	$224.91	$224.90	$224.90
Purchase #3	$241.69	13.599%	$274.5574	$274.56	$274.55	$274.60
Purchase #4	$200.30	5.166%	$210.6475	$210.65	$210.65	$210.60
Purchase #5	$29.53	9.181%	$32.2411	$32.24	$32.25	$32.20
Purchase #6	$184.91	3.475%	$191.3356	$191.34	$191.35	$191.30
Purchase #7	$60.73	13.829%	$69.1284	$69.13	$69.15	$69.10
7 purchase totals =	$1,016.29		$1,102.5092	$1,102.52	$1,102.55	$1,102.40