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	$133.45	13.395%	$151.3256	$151.33	$151.35	$151.30
Purchase #2	$43.55	4.316%	$45.4296	$45.43	$45.45	$45.40
Purchase #3	$207.53	11.693%	$231.7965	$231.80	$231.80	$231.80
Purchase #4	$26.58	6.682%	$28.3561	$28.36	$28.35	$28.40
Purchase #5	$181.34	4.468%	$189.4423	$189.44	$189.45	$189.40
Purchase #6	$23.49	8.415%	$25.4667	$25.47	$25.45	$25.50
Purchase #7	$136.30	10.362%	$150.4234	$150.42	$150.40	$150.40
7 purchase totals =	$752.24		$822.2402	$822.25	$822.25	$822.20