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	$241.84	7.219%	$259.2984	$259.30	$259.30	$259.30
Purchase #2	$169.68	12.309%	$190.5659	$190.57	$190.55	$190.60
Purchase #3	$99.38	11.195%	$110.5056	$110.51	$110.50	$110.50
Purchase #4	$66.48	8.680%	$72.2505	$72.25	$72.25	$72.30
Purchase #5	$218.73	11.370%	$243.5996	$243.60	$243.60	$243.60
Purchase #6	$150.94	13.632%	$171.5161	$171.52	$171.50	$171.50
Purchase #7	$199.56	8.548%	$216.6184	$216.62	$216.60	$216.60
7 purchase totals =	$1,146.61		$1,264.3545	$1,264.37	$1,264.30	$1,264.40