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	$175.87	7.364%	$188.8211	$188.82	$188.80	$188.80
Purchase #2	$144.39	4.112%	$150.3273	$150.33	$150.35	$150.30
Purchase #3	$162.92	10.755%	$180.442	$180.44	$180.45	$180.40
Purchase #4	$55.40	9.282%	$60.5422	$60.54	$60.55	$60.50
Purchase #5	$123.54	13.438%	$140.1413	$140.14	$140.15	$140.10
Purchase #6	$209.87	4.762%	$219.864	$219.86	$219.85	$219.90
Purchase #7	$25.76	11.655%	$28.7623	$28.76	$28.75	$28.80
7 purchase totals =	$897.75		$968.9002	$968.89	$968.90	$968.80