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	$100.89	3.685%	$104.6078	$104.61	$104.60	$104.60
Purchase #2	$193.98	12.249%	$217.7406	$217.74	$217.75	$217.70
Purchase #3	$152.30	9.206%	$166.3207	$166.32	$166.30	$166.30
Purchase #4	$192.60	12.117%	$215.9373	$215.94	$215.95	$215.90
Purchase #5	$70.49	11.418%	$78.5385	$78.54	$78.55	$78.50
Purchase #6	$167.27	13.655%	$190.1107	$190.11	$190.10	$190.10
Purchase #7	$7.38	11.684%	$8.2423	$8.24	$8.25	$8.20
7 purchase totals =	$884.91		$981.4979	$981.50	$981.50	$981.30