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	$149.71	13.540%	$169.9807	$169.98	$170.00	$170.00
Purchase #2	$234.74	3.362%	$242.632	$242.63	$242.65	$242.60
Purchase #3	$29.92	12.234%	$33.5804	$33.58	$33.60	$33.60
Purchase #4	$90.64	4.582%	$94.7931	$94.79	$94.80	$94.80
Purchase #5	$58.69	5.117%	$61.6932	$61.69	$61.70	$61.70
Purchase #6	$84.78	6.190%	$90.0279	$90.03	$90.05	$90.00
Purchase #7	$33.66	12.184%	$37.7611	$37.76	$37.75	$37.80
7 purchase totals =	$682.14		$730.4684	$730.46	$730.55	$730.50