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	$138.48	6.387%	$147.3247	$147.32	$147.30	$147.30
Purchase #2	$130.78	11.621%	$145.9779	$145.98	$146.00	$146.00
Purchase #3	$244.28	12.111%	$273.8648	$273.86	$273.85	$273.90
Purchase #4	$67.48	6.471%	$71.8466	$71.85	$71.85	$71.80
Purchase #5	$153.98	7.575%	$165.644	$165.64	$165.65	$165.60
Purchase #6	$46.66	7.391%	$50.1086	$50.11	$50.10	$50.10
Purchase #7	$38.94	11.534%	$43.4313	$43.43	$43.45	$43.40
7 purchase totals =	$820.60		$898.1979	$898.19	$898.20	$898.10