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	$113.55	8.576%	$123.288	$123.29	$123.30	$123.30
Purchase #2	$139.66	4.229%	$145.5662	$145.57	$145.55	$145.60
Purchase #3	$34.56	11.459%	$38.5202	$38.52	$38.50	$38.50
Purchase #4	$30.49	8.804%	$33.1743	$33.17	$33.15	$33.20
Purchase #5	$142.27	10.588%	$157.3335	$157.33	$157.35	$157.30
Purchase #6	$101.98	12.704%	$114.9355	$114.94	$114.95	$114.90
Purchase #7	$230.46	11.258%	$256.4052	$256.41	$256.40	$256.40
7 purchase totals =	$792.97		$869.2229	$869.23	$869.20	$869.20