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	$132.70	6.430%	$141.2326	$141.23	$141.25	$141.20
Purchase #2	$85.31	5.741%	$90.2076	$90.21	$90.20	$90.20
Purchase #3	$237.26	7.446%	$254.9264	$254.93	$254.95	$254.90
Purchase #4	$42.86	5.206%	$45.0913	$45.09	$45.10	$45.10
Purchase #5	$96.67	3.340%	$99.8988	$99.90	$99.90	$99.90
Purchase #6	$76.86	7.774%	$82.8351	$82.84	$82.85	$82.80
Purchase #7	$169.80	7.109%	$181.8711	$181.87	$181.85	$181.90
7 purchase totals =	$841.46		$896.0629	$896.07	$896.10	$896.00