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	$31.62	4.873%	$33.1608	$33.16	$33.15	$33.20
Purchase #2	$157.28	9.720%	$172.5676	$172.57	$172.55	$172.60
Purchase #3	$129.49	8.312%	$140.2532	$140.25	$140.25	$140.30
Purchase #4	$43.95	3.670%	$45.563	$45.56	$45.55	$45.60
Purchase #5	$239.41	7.292%	$256.8678	$256.87	$256.85	$256.90
Purchase #6	$103.79	11.281%	$115.4985	$115.50	$115.50	$115.50
Purchase #7	$210.94	13.257%	$238.9043	$238.90	$238.90	$238.90
7 purchase totals =	$916.48		$1,002.8152	$1,002.81	$1,002.75	$1,003.00