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	$9.72	3.440%	$10.0544	$10.05	$10.05	$10.10
Purchase #2	$66.42	8.293%	$71.9282	$71.93	$71.95	$71.90
Purchase #3	$148.63	7.357%	$159.5647	$159.56	$159.55	$159.60
Purchase #4	$55.40	3.739%	$57.4714	$57.47	$57.45	$57.50
Purchase #5	$165.31	13.755%	$188.0484	$188.05	$188.05	$188.00
Purchase #6	$211.82	8.272%	$229.3418	$229.34	$229.35	$229.30
Purchase #7	$152.48	8.456%	$165.3737	$165.37	$165.35	$165.40
7 purchase totals =	$809.78		$881.7826	$881.77	$881.75	$881.80