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	$19.50	8.400%	$21.138	$21.14	$21.15	$21.10
Purchase #2	$84.44	7.487%	$90.762	$90.76	$90.75	$90.80
Purchase #3	$84.46	12.625%	$95.1231	$95.12	$95.10	$95.10
Purchase #4	$96.68	4.186%	$100.727	$100.73	$100.75	$100.70
Purchase #5	$223.34	5.115%	$234.7638	$234.76	$234.75	$234.80
Purchase #6	$137.26	6.663%	$146.4056	$146.41	$146.40	$146.40
Purchase #7	$97.47	9.360%	$106.5932	$106.59	$106.60	$106.60
7 purchase totals =	$743.15		$795.5127	$795.51	$795.50	$795.50