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	$152.36	3.588%	$157.8267	$157.83	$157.85	$157.80
Purchase #2	$181.51	10.103%	$199.848	$199.85	$199.85	$199.80
Purchase #3	$162.31	11.414%	$180.8361	$180.84	$180.85	$180.80
Purchase #4	$18.61	10.130%	$20.4952	$20.50	$20.50	$20.50
Purchase #5	$28.69	12.495%	$32.2748	$32.27	$32.25	$32.30
Purchase #6	$219.28	6.562%	$233.6692	$233.67	$233.65	$233.70
Purchase #7	$95.35	10.531%	$105.3913	$105.39	$105.40	$105.40
7 purchase totals =	$858.11		$930.3413	$930.35	$930.35	$930.30