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	$134.58	8.791%	$146.4109	$146.41	$146.40	$146.40
Purchase #2	$193.80	11.790%	$216.649	$216.65	$216.65	$216.60
Purchase #3	$91.83	4.401%	$95.8714	$95.87	$95.85	$95.90
Purchase #4	$61.30	13.777%	$69.7453	$69.75	$69.75	$69.70
Purchase #5	$56.52	8.582%	$61.3705	$61.37	$61.35	$61.40
Purchase #6	$12.69	8.162%	$13.7258	$13.73	$13.75	$13.70
Purchase #7	$86.80	3.174%	$89.555	$89.56	$89.55	$89.60
7 purchase totals =	$637.52		$693.3279	$693.34	$693.30	$693.30