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	$223.71	3.362%	$231.2311	$231.23	$231.25	$231.20
Purchase #2	$80.77	11.854%	$90.3445	$90.34	$90.35	$90.30
Purchase #3	$139.89	9.580%	$153.2915	$153.29	$153.30	$153.30
Purchase #4	$106.60	7.490%	$114.5843	$114.58	$114.60	$114.60
Purchase #5	$244.50	8.306%	$264.8082	$264.81	$264.80	$264.80
Purchase #6	$160.60	9.437%	$175.7558	$175.76	$175.75	$175.80
Purchase #7	$126.94	4.347%	$132.4581	$132.46	$132.45	$132.50
7 purchase totals =	$1,083.01		$1,162.4735	$1,162.47	$1,162.50	$1,162.50