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	$28.61	4.616%	$29.9306	$29.93	$29.95	$29.90
Purchase #2	$228.33	13.130%	$258.3097	$258.31	$258.30	$258.30
Purchase #3	$88.62	11.811%	$99.0869	$99.09	$99.10	$99.10
Purchase #4	$63.46	6.178%	$67.3806	$67.38	$67.40	$67.40
Purchase #5	$126.87	13.796%	$144.373	$144.37	$144.35	$144.40
Purchase #6	$148.47	7.539%	$159.6632	$159.66	$159.65	$159.70
Purchase #7	$116.86	12.428%	$131.3834	$131.38	$131.40	$131.40
7 purchase totals =	$801.22		$890.1274	$890.12	$890.15	$890.20