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	$109.91	9.143%	$119.9591	$119.96	$119.95	$120.00
Purchase #2	$246.65	11.680%	$275.4587	$275.46	$275.45	$275.50
Purchase #3	$160.45	3.251%	$165.6662	$165.67	$165.65	$165.70
Purchase #4	$30.45	3.472%	$31.5072	$31.51	$31.50	$31.50
Purchase #5	$145.49	9.462%	$159.2563	$159.26	$159.25	$159.30
Purchase #6	$137.45	9.310%	$150.2466	$150.25	$150.25	$150.20
Purchase #7	$157.90	4.642%	$165.2297	$165.23	$165.25	$165.20
7 purchase totals =	$988.30		$1,067.3238	$1,067.34	$1,067.30	$1,067.40