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	$221.87	7.672%	$238.8919	$238.89	$238.90	$238.90
Purchase #2	$149.71	6.560%	$159.531	$159.53	$159.55	$159.50
Purchase #3	$71.46	10.272%	$78.8004	$78.80	$78.80	$78.80
Purchase #4	$162.75	5.221%	$171.2472	$171.25	$171.25	$171.20
Purchase #5	$197.33	11.710%	$220.4373	$220.44	$220.45	$220.40
Purchase #6	$48.71	3.731%	$50.5274	$50.53	$50.55	$50.50
Purchase #7	$52.69	6.380%	$56.0516	$56.05	$56.05	$56.10
7 purchase totals =	$904.52		$975.4868	$975.49	$975.55	$975.40