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	$91.62	10.121%	$100.8929	$100.89	$100.90	$100.90
Purchase #2	$139.64	9.599%	$153.044	$153.04	$153.05	$153.00
Purchase #3	$136.73	5.290%	$143.963	$143.96	$143.95	$144.00
Purchase #4	$108.44	5.590%	$114.5018	$114.50	$114.50	$114.50
Purchase #5	$34.94	8.524%	$37.9183	$37.92	$37.90	$37.90
Purchase #6	$63.82	12.308%	$71.675	$71.68	$71.70	$71.70
Purchase #7	$93.29	12.300%	$104.7647	$104.76	$104.75	$104.80
7 purchase totals =	$668.48		$726.7597	$726.75	$726.75	$726.80