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	$95.94	6.441%	$102.1195	$102.12	$102.10	$102.10
Purchase #2	$52.51	13.139%	$59.4093	$59.41	$59.40	$59.40
Purchase #3	$80.73	12.143%	$90.533	$90.53	$90.55	$90.50
Purchase #4	$211.94	9.240%	$231.5233	$231.52	$231.50	$231.50
Purchase #5	$212.58	5.271%	$223.7851	$223.79	$223.80	$223.80
Purchase #6	$193.54	10.649%	$214.1501	$214.15	$214.15	$214.20
Purchase #7	$57.64	11.350%	$64.1821	$64.18	$64.20	$64.20
7 purchase totals =	$904.88		$985.7024	$985.70	$985.70	$985.70