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	$247.74	3.490%	$256.3861	$256.39	$256.40	$256.40
Purchase #2	$187.48	6.744%	$200.1237	$200.12	$200.10	$200.10
Purchase #3	$140.29	7.269%	$150.4877	$150.49	$150.50	$150.50
Purchase #4	$13.73	12.541%	$15.4519	$15.45	$15.45	$15.50
Purchase #5	$22.62	6.787%	$24.1552	$24.16	$24.15	$24.20
Purchase #6	$96.49	3.807%	$100.1634	$100.16	$100.15	$100.20
Purchase #7	$34.72	10.684%	$38.4295	$38.43	$38.45	$38.40
7 purchase totals =	$743.07		$785.1975	$785.20	$785.20	$785.30