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	$9.29	12.118%	$10.4158	$10.42	$10.40	$10.40
Purchase #2	$6.33	13.406%	$7.1786	$7.18	$7.20	$7.20
Purchase #3	$199.62	5.515%	$210.629	$210.63	$210.65	$210.60
Purchase #4	$33.56	11.320%	$37.359	$37.36	$37.35	$37.40
Purchase #5	$38.91	4.773%	$40.7672	$40.77	$40.75	$40.80
Purchase #6	$169.52	4.155%	$176.5636	$176.56	$176.55	$176.60
Purchase #7	$63.39	7.221%	$67.9674	$67.97	$67.95	$68.00
7 purchase totals =	$520.62		$550.8806	$550.89	$550.85	$551.00