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	$121.58	4.638%	$127.2189	$127.22	$127.20	$127.20
Purchase #2	$67.29	5.863%	$71.2352	$71.24	$71.25	$71.20
Purchase #3	$109.66	12.442%	$123.3039	$123.30	$123.30	$123.30
Purchase #4	$33.46	3.547%	$34.6468	$34.65	$34.65	$34.60
Purchase #5	$65.33	9.777%	$71.7173	$71.72	$71.70	$71.70
Purchase #6	$151.93	11.406%	$169.2591	$169.26	$169.25	$169.30
Purchase #7	$176.47	3.212%	$182.1382	$182.14	$182.15	$182.10
7 purchase totals =	$725.72		$779.5194	$779.53	$779.50	$779.40