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	$19.55	6.248%	$20.7715	$20.77	$20.75	$20.80
Purchase #2	$181.79	4.315%	$189.6342	$189.63	$189.65	$189.60
Purchase #3	$113.82	10.746%	$126.0511	$126.05	$126.05	$126.10
Purchase #4	$228.73	6.195%	$242.8998	$242.90	$242.90	$242.90
Purchase #5	$109.26	13.289%	$123.7796	$123.78	$123.80	$123.80
Purchase #6	$227.92	11.593%	$254.3428	$254.34	$254.35	$254.30
Purchase #7	$53.91	13.489%	$61.1819	$61.18	$61.20	$61.20
7 purchase totals =	$934.98		$1,018.6609	$1,018.65	$1,018.70	$1,018.70