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	$172.77	4.428%	$180.4203	$180.42	$180.40	$180.40
Purchase #2	$142.96	9.637%	$156.7371	$156.74	$156.75	$156.70
Purchase #3	$92.78	7.156%	$99.4193	$99.42	$99.40	$99.40
Purchase #4	$146.36	7.430%	$157.2345	$157.23	$157.25	$157.20
Purchase #5	$131.26	4.575%	$137.2651	$137.27	$137.25	$137.30
Purchase #6	$56.59	9.291%	$61.8478	$61.85	$61.85	$61.80
Purchase #7	$153.98	7.742%	$165.9011	$165.90	$165.90	$165.90
7 purchase totals =	$896.70		$958.8252	$958.83	$958.80	$958.70