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	$54.33	10.120%	$59.8282	$59.83	$59.85	$59.80
Purchase #2	$34.47	5.614%	$36.4051	$36.41	$36.40	$36.40
Purchase #3	$104.93	4.120%	$109.2531	$109.25	$109.25	$109.30
Purchase #4	$54.87	8.225%	$59.3831	$59.38	$59.40	$59.40
Purchase #5	$46.35	9.310%	$50.6652	$50.67	$50.65	$50.70
Purchase #6	$9.69	4.860%	$10.1609	$10.16	$10.15	$10.20
Purchase #7	$206.31	10.118%	$227.1844	$227.18	$227.20	$227.20
7 purchase totals =	$510.95		$552.8800	$552.88	$552.90	$553.00