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	$250.58	7.183%	$268.5792	$268.58	$268.60	$268.60
Purchase #2	$179.72	11.125%	$199.7139	$199.71	$199.70	$199.70
Purchase #3	$168.33	8.731%	$183.0269	$183.03	$183.05	$183.00
Purchase #4	$99.47	8.830%	$108.2532	$108.25	$108.25	$108.30
Purchase #5	$240.48	10.150%	$264.8887	$264.89	$264.90	$264.90
Purchase #6	$175.39	11.516%	$195.5879	$195.59	$195.60	$195.60
Purchase #7	$186.58	5.394%	$196.6441	$196.64	$196.65	$196.60
7 purchase totals =	$1,300.55		$1,416.6939	$1,416.69	$1,416.75	$1,416.70