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	$248.88	10.544%	$275.1219	$275.12	$275.10	$275.10
Purchase #2	$53.70	12.296%	$60.303	$60.30	$60.30	$60.30
Purchase #3	$77.84	9.485%	$85.2231	$85.22	$85.20	$85.20
Purchase #4	$74.55	4.251%	$77.7191	$77.72	$77.70	$77.70
Purchase #5	$19.85	6.539%	$21.148	$21.15	$21.15	$21.10
Purchase #6	$208.50	4.683%	$218.2641	$218.26	$218.25	$218.30
Purchase #7	$250.71	9.740%	$275.1292	$275.13	$275.15	$275.10
7 purchase totals =	$934.03		$1,012.9084	$1,012.90	$1,012.85	$1,012.80