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	$29.30	13.449%	$33.2406	$33.24	$33.25	$33.20
Purchase #2	$221.66	13.521%	$251.6306	$251.63	$251.65	$251.60
Purchase #3	$105.90	9.757%	$116.2327	$116.23	$116.25	$116.20
Purchase #4	$74.50	5.408%	$78.529	$78.53	$78.55	$78.50
Purchase #5	$14.31	5.722%	$15.1288	$15.13	$15.15	$15.10
Purchase #6	$125.54	11.449%	$139.9131	$139.91	$139.90	$139.90
Purchase #7	$232.33	4.649%	$243.131	$243.13	$243.15	$243.10
7 purchase totals =	$803.54		$877.8058	$877.80	$877.90	$877.60