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	$42.66	6.323%	$45.3574	$45.36	$45.35	$45.40
Purchase #2	$234.42	10.544%	$259.1372	$259.14	$259.15	$259.10
Purchase #3	$87.45	3.479%	$90.4924	$90.49	$90.50	$90.50
Purchase #4	$54.93	5.426%	$57.9105	$57.91	$57.90	$57.90
Purchase #5	$16.40	4.850%	$17.1954	$17.20	$17.20	$17.20
Purchase #6	$53.54	3.741%	$55.5429	$55.54	$55.55	$55.50
Purchase #7	$185.95	12.785%	$209.7237	$209.72	$209.70	$209.70
7 purchase totals =	$675.35		$735.3595	$735.36	$735.35	$735.30