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	$64.85	9.783%	$71.1943	$71.19	$71.20	$71.20
Purchase #2	$77.34	13.383%	$87.6904	$87.69	$87.70	$87.70
Purchase #3	$34.81	6.624%	$37.1158	$37.12	$37.10	$37.10
Purchase #4	$242.70	13.610%	$275.7315	$275.73	$275.75	$275.70
Purchase #5	$79.89	8.778%	$86.9027	$86.90	$86.90	$86.90
Purchase #6	$249.38	7.734%	$268.667	$268.67	$268.65	$268.70
Purchase #7	$82.91	7.570%	$89.1863	$89.19	$89.20	$89.20
7 purchase totals =	$831.88		$916.4880	$916.49	$916.50	$916.50