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	$77.90	9.764%	$85.5062	$85.51	$85.50	$85.50
Purchase #2	$109.40	13.703%	$124.3911	$124.39	$124.40	$124.40
Purchase #3	$108.53	7.279%	$116.4299	$116.43	$116.45	$116.40
Purchase #4	$176.71	3.112%	$182.2092	$182.21	$182.20	$182.20
Purchase #5	$236.59	7.503%	$254.3413	$254.34	$254.35	$254.30
Purchase #6	$143.82	8.604%	$156.1943	$156.19	$156.20	$156.20
Purchase #7	$18.62	13.728%	$21.1762	$21.18	$21.20	$21.20
7 purchase totals =	$871.57		$940.2482	$940.25	$940.30	$940.20