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	$247.64	10.373%	$273.3277	$273.33	$273.35	$273.30
Purchase #2	$187.67	4.692%	$196.4755	$196.48	$196.50	$196.50
Purchase #3	$221.65	12.841%	$250.1121	$250.11	$250.10	$250.10
Purchase #4	$142.85	3.246%	$147.4869	$147.49	$147.50	$147.50
Purchase #5	$107.58	5.488%	$113.484	$113.48	$113.50	$113.50
Purchase #6	$51.88	8.869%	$56.4812	$56.48	$56.50	$56.50
Purchase #7	$51.30	4.247%	$53.4787	$53.48	$53.50	$53.50
7 purchase totals =	$1,010.57		$1,090.8461	$1,090.85	$1,090.95	$1,090.90