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	$49.25	7.700%	$53.0423	$53.04	$53.05	$53.00
Purchase #2	$100.78	12.198%	$113.0731	$113.07	$113.05	$113.10
Purchase #3	$200.75	9.702%	$220.2268	$220.23	$220.25	$220.20
Purchase #4	$167.58	9.486%	$183.4766	$183.48	$183.50	$183.50
Purchase #5	$16.86	9.864%	$18.5231	$18.52	$18.50	$18.50
Purchase #6	$47.56	10.787%	$52.6903	$52.69	$52.70	$52.70
Purchase #7	$57.33	4.457%	$59.8852	$59.89	$59.90	$59.90
7 purchase totals =	$640.11		$700.9174	$700.92	$700.95	$700.90