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	$48.78	4.508%	$50.979	$50.98	$51.00	$51.00
Purchase #2	$127.99	10.194%	$141.0373	$141.04	$141.05	$141.00
Purchase #3	$170.66	10.850%	$189.1766	$189.18	$189.20	$189.20
Purchase #4	$31.57	3.851%	$32.7858	$32.79	$32.80	$32.80
Purchase #5	$154.72	6.673%	$165.0445	$165.04	$165.05	$165.00
Purchase #6	$107.77	8.394%	$116.8162	$116.82	$116.80	$116.80
Purchase #7	$124.82	4.412%	$130.3271	$130.33	$130.35	$130.30
7 purchase totals =	$766.31		$826.1665	$826.18	$826.25	$826.10