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	$71.89	3.587%	$74.4687	$74.47	$74.45	$74.50
Purchase #2	$69.93	9.124%	$76.3104	$76.31	$76.30	$76.30
Purchase #3	$18.54	9.163%	$20.2388	$20.24	$20.25	$20.20
Purchase #4	$200.75	10.352%	$221.5316	$221.53	$221.55	$221.50
Purchase #5	$108.76	10.238%	$119.8948	$119.89	$119.90	$119.90
Purchase #6	$86.57	6.203%	$91.9399	$91.94	$91.95	$91.90
Purchase #7	$137.58	4.834%	$144.2306	$144.23	$144.25	$144.20
7 purchase totals =	$694.02		$748.6148	$748.61	$748.65	$748.50