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	$45.93	9.210%	$50.1602	$50.16	$50.15	$50.20
Purchase #2	$178.41	12.559%	$200.8165	$200.82	$200.80	$200.80
Purchase #3	$215.88	4.256%	$225.0679	$225.07	$225.05	$225.10
Purchase #4	$100.91	5.427%	$106.3864	$106.39	$106.40	$106.40
Purchase #5	$172.54	3.821%	$179.1328	$179.13	$179.15	$179.10
Purchase #6	$173.32	12.632%	$195.2138	$195.21	$195.20	$195.20
Purchase #7	$125.90	3.401%	$130.1819	$130.18	$130.20	$130.20
7 purchase totals =	$1,012.89		$1,086.9595	$1,086.96	$1,086.95	$1,087.00