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	$54.40	3.652%	$56.3867	$56.39	$56.40	$56.40
Purchase #2	$156.56	10.461%	$172.9377	$172.94	$172.95	$172.90
Purchase #3	$182.94	3.408%	$189.1746	$189.17	$189.15	$189.20
Purchase #4	$25.56	9.366%	$27.9539	$27.95	$27.95	$28.00
Purchase #5	$191.71	9.111%	$209.1767	$209.18	$209.20	$209.20
Purchase #6	$37.76	13.561%	$42.8806	$42.88	$42.90	$42.90
Purchase #7	$57.70	11.540%	$64.3586	$64.36	$64.35	$64.40
7 purchase totals =	$706.63		$762.8688	$762.87	$762.90	$763.00