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	$129.78	13.173%	$146.8759	$146.88	$146.90	$146.90
Purchase #2	$56.59	6.854%	$60.4687	$60.47	$60.45	$60.50
Purchase #3	$137.89	4.252%	$143.7531	$143.75	$143.75	$143.80
Purchase #4	$79.64	9.656%	$87.33	$87.33	$87.35	$87.30
Purchase #5	$87.61	4.358%	$91.428	$91.43	$91.45	$91.40
Purchase #6	$69.69	3.363%	$72.0337	$72.03	$72.05	$72.00
Purchase #7	$7.95	11.578%	$8.8705	$8.87	$8.85	$8.90
7 purchase totals =	$569.15		$610.7599	$610.76	$610.80	$610.80