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	$118.37	4.156%	$123.2895	$123.29	$123.30	$123.30
Purchase #2	$78.82	13.605%	$89.5435	$89.54	$89.55	$89.50
Purchase #3	$221.63	13.276%	$251.0536	$251.05	$251.05	$251.10
Purchase #4	$237.35	9.424%	$259.7179	$259.72	$259.70	$259.70
Purchase #5	$146.25	9.576%	$160.2549	$160.25	$160.25	$160.30
Purchase #6	$135.63	4.625%	$141.9029	$141.90	$141.90	$141.90
Purchase #7	$181.87	5.443%	$191.7692	$191.77	$191.75	$191.80
7 purchase totals =	$1,119.92		$1,217.5315	$1,217.52	$1,217.50	$1,217.60