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	$86.88	13.277%	$98.4151	$98.42	$98.40	$98.40
Purchase #2	$80.89	10.836%	$89.6552	$89.66	$89.65	$89.70
Purchase #3	$58.25	9.331%	$63.6853	$63.69	$63.70	$63.70
Purchase #4	$167.79	10.725%	$185.7855	$185.79	$185.80	$185.80
Purchase #5	$219.42	11.578%	$244.8244	$244.82	$244.80	$244.80
Purchase #6	$119.29	9.307%	$130.3923	$130.39	$130.40	$130.40
Purchase #7	$36.52	10.680%	$40.4203	$40.42	$40.40	$40.40
7 purchase totals =	$769.04		$853.1781	$853.19	$853.15	$853.20