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	$87.90	13.419%	$99.6953	$99.70	$99.70	$99.70
Purchase #2	$121.62	5.177%	$127.9163	$127.92	$127.90	$127.90
Purchase #3	$77.95	4.183%	$81.2106	$81.21	$81.20	$81.20
Purchase #4	$246.86	9.197%	$269.5637	$269.56	$269.55	$269.60
Purchase #5	$90.75	8.319%	$98.2995	$98.30	$98.30	$98.30
Purchase #6	$247.47	11.165%	$275.1	$275.10	$275.10	$275.10
Purchase #7	$169.87	5.554%	$179.3046	$179.30	$179.30	$179.30
7 purchase totals =	$1,042.42		$1,131.0900	$1,131.09	$1,131.05	$1,131.10