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	$243.77	12.344%	$273.861	$273.86	$273.85	$273.90
Purchase #2	$54.30	5.600%	$57.3408	$57.34	$57.35	$57.30
Purchase #3	$244.94	3.700%	$254.0028	$254.00	$254.00	$254.00
Purchase #4	$45.41	3.654%	$47.0693	$47.07	$47.05	$47.10
Purchase #5	$133.33	4.223%	$138.9605	$138.96	$138.95	$139.00
Purchase #6	$214.60	4.114%	$223.4286	$223.43	$223.45	$223.40
Purchase #7	$59.77	3.255%	$61.7155	$61.72	$61.70	$61.70
7 purchase totals =	$996.12		$1,056.3785	$1,056.38	$1,056.35	$1,056.40