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	$93.37	5.104%	$98.1356	$98.14	$98.15	$98.10
Purchase #2	$71.68	4.310%	$74.7694	$74.77	$74.75	$74.80
Purchase #3	$138.76	5.182%	$145.9505	$145.95	$145.95	$146.00
Purchase #4	$39.54	7.571%	$42.5336	$42.53	$42.55	$42.50
Purchase #5	$100.41	11.866%	$112.3247	$112.32	$112.30	$112.30
Purchase #6	$172.69	4.587%	$180.6113	$180.61	$180.60	$180.60
Purchase #7	$134.61	4.428%	$140.5705	$140.57	$140.55	$140.60
7 purchase totals =	$751.06		$794.8956	$794.89	$794.85	$794.90