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	$22.88	7.628%	$24.6253	$24.63	$24.65	$24.60
Purchase #2	$212.40	5.418%	$223.9078	$223.91	$223.90	$223.90
Purchase #3	$42.81	5.785%	$45.2866	$45.29	$45.30	$45.30
Purchase #4	$151.81	4.851%	$159.1743	$159.17	$159.15	$159.20
Purchase #5	$180.54	10.145%	$198.8558	$198.86	$198.85	$198.90
Purchase #6	$250.32	11.471%	$279.0342	$279.03	$279.05	$279.00
Purchase #7	$130.85	3.433%	$135.3421	$135.34	$135.35	$135.30
7 purchase totals =	$991.61		$1,066.2261	$1,066.23	$1,066.25	$1,066.20