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	$146.86	12.475%	$165.1808	$165.18	$165.20	$165.20
Purchase #2	$68.98	8.232%	$74.6584	$74.66	$74.65	$74.70
Purchase #3	$84.56	12.133%	$94.8197	$94.82	$94.80	$94.80
Purchase #4	$123.34	5.213%	$129.7697	$129.77	$129.75	$129.80
Purchase #5	$231.25	6.111%	$245.3817	$245.38	$245.40	$245.40
Purchase #6	$75.71	13.788%	$86.1489	$86.15	$86.15	$86.10
Purchase #7	$196.83	13.267%	$222.9434	$222.94	$222.95	$222.90
7 purchase totals =	$927.53		$1,018.9026	$1,018.90	$1,018.90	$1,018.90