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	$24.91	13.345%	$28.2342	$28.23	$28.25	$28.20
Purchase #2	$98.57	8.487%	$106.9356	$106.94	$106.95	$106.90
Purchase #3	$157.30	3.445%	$162.719	$162.72	$162.70	$162.70
Purchase #4	$86.64	11.762%	$96.8306	$96.83	$96.85	$96.80
Purchase #5	$85.69	10.740%	$94.8931	$94.89	$94.90	$94.90
Purchase #6	$77.71	12.169%	$87.1665	$87.17	$87.15	$87.20
Purchase #7	$164.82	12.628%	$185.6335	$185.63	$185.65	$185.60
7 purchase totals =	$695.64		$762.4125	$762.41	$762.45	$762.30