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	$240.89	13.505%	$273.4222	$273.42	$273.40	$273.40
Purchase #2	$192.35	3.659%	$199.3881	$199.39	$199.40	$199.40
Purchase #3	$247.88	8.834%	$269.7777	$269.78	$269.80	$269.80
Purchase #4	$129.56	11.236%	$144.1174	$144.12	$144.10	$144.10
Purchase #5	$95.49	6.821%	$102.0034	$102.00	$102.00	$102.00
Purchase #6	$123.32	10.300%	$136.022	$136.02	$136.00	$136.00
Purchase #7	$55.55	6.238%	$59.0152	$59.02	$59.00	$59.00
7 purchase totals =	$1,085.04		$1,183.7460	$1,183.75	$1,183.70	$1,183.70