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	$98.31	6.207%	$104.4121	$104.41	$104.40	$104.40
Purchase #2	$69.86	5.359%	$73.6038	$73.60	$73.60	$73.60
Purchase #3	$214.83	8.587%	$233.2775	$233.28	$233.30	$233.30
Purchase #4	$54.73	11.757%	$61.1646	$61.16	$61.15	$61.20
Purchase #5	$29.49	13.630%	$33.5095	$33.51	$33.50	$33.50
Purchase #6	$147.68	12.761%	$166.5254	$166.53	$166.55	$166.50
Purchase #7	$131.41	12.482%	$147.8126	$147.81	$147.80	$147.80
7 purchase totals =	$746.31		$820.3055	$820.30	$820.30	$820.30