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	$23.73	4.228%	$24.7333	$24.73	$24.75	$24.70
Purchase #2	$210.27	9.226%	$229.6695	$229.67	$229.65	$229.70
Purchase #3	$45.84	10.485%	$50.6463	$50.65	$50.65	$50.60
Purchase #4	$82.59	8.816%	$89.8711	$89.87	$89.85	$89.90
Purchase #5	$39.64	13.554%	$45.0128	$45.01	$45.00	$45.00
Purchase #6	$17.61	5.412%	$18.5631	$18.56	$18.55	$18.60
Purchase #7	$130.39	8.435%	$141.3884	$141.39	$141.40	$141.40
7 purchase totals =	$550.07		$599.8845	$599.88	$599.85	$599.90