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	$22.50	12.109%	$25.2245	$25.22	$25.20	$25.20
Purchase #2	$156.32	12.354%	$175.6318	$175.63	$175.65	$175.60
Purchase #3	$159.84	3.504%	$165.4408	$165.44	$165.45	$165.40
Purchase #4	$136.94	10.216%	$150.9298	$150.93	$150.95	$150.90
Purchase #5	$125.79	9.621%	$137.8923	$137.89	$137.90	$137.90
Purchase #6	$119.79	6.492%	$127.5668	$127.57	$127.55	$127.60
Purchase #7	$95.93	10.110%	$105.6285	$105.63	$105.65	$105.60
7 purchase totals =	$817.11		$888.3145	$888.31	$888.35	$888.20