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	$12.53	3.162%	$12.9262	$12.93	$12.95	$12.90
Purchase #2	$197.50	12.511%	$222.2092	$222.21	$222.20	$222.20
Purchase #3	$119.77	8.753%	$130.2535	$130.25	$130.25	$130.30
Purchase #4	$42.99	6.196%	$45.6537	$45.65	$45.65	$45.70
Purchase #5	$154.35	12.785%	$174.0836	$174.08	$174.10	$174.10
Purchase #6	$131.82	5.621%	$139.2296	$139.23	$139.25	$139.20
Purchase #7	$195.35	11.739%	$218.2821	$218.28	$218.30	$218.30
7 purchase totals =	$854.31		$942.6379	$942.63	$942.70	$942.70