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	$92.42	12.413%	$103.8921	$103.89	$103.90	$103.90
Purchase #2	$54.63	11.674%	$61.0075	$61.01	$61.00	$61.00
Purchase #3	$64.76	11.369%	$72.1226	$72.12	$72.10	$72.10
Purchase #4	$136.50	8.314%	$147.8486	$147.85	$147.85	$147.80
Purchase #5	$214.42	12.350%	$240.9009	$240.90	$240.90	$240.90
Purchase #6	$79.52	6.479%	$84.6721	$84.67	$84.65	$84.70
Purchase #7	$24.85	13.774%	$28.2728	$28.27	$28.25	$28.30
7 purchase totals =	$667.10		$738.7166	$738.71	$738.65	$738.70