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	$13.71	11.773%	$15.3241	$15.32	$15.30	$15.30
Purchase #2	$60.65	4.160%	$63.173	$63.17	$63.15	$63.20
Purchase #3	$75.73	3.779%	$78.5918	$78.59	$78.60	$78.60
Purchase #4	$140.37	7.728%	$151.2178	$151.22	$151.20	$151.20
Purchase #5	$81.55	6.137%	$86.5547	$86.55	$86.55	$86.60
Purchase #6	$229.82	6.143%	$243.9378	$243.94	$243.95	$243.90
Purchase #7	$91.32	3.420%	$94.4431	$94.44	$94.45	$94.40
7 purchase totals =	$693.15		$733.2423	$733.23	$733.20	$733.20