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	$144.71	13.595%	$164.3833	$164.38	$164.40	$164.40
Purchase #2	$41.85	9.674%	$45.8986	$45.90	$45.90	$45.90
Purchase #3	$14.29	6.326%	$15.194	$15.19	$15.20	$15.20
Purchase #4	$130.74	12.537%	$147.1309	$147.13	$147.15	$147.10
Purchase #5	$233.27	9.605%	$255.6756	$255.68	$255.70	$255.70
Purchase #6	$237.56	11.366%	$264.5611	$264.56	$264.55	$264.60
Purchase #7	$78.62	3.184%	$81.1233	$81.12	$81.10	$81.10
7 purchase totals =	$881.04		$973.9668	$973.96	$974.00	$974.00