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	$96.47	13.295%	$109.2957	$109.30	$109.30	$109.30
Purchase #2	$153.54	8.824%	$167.0884	$167.09	$167.10	$167.10
Purchase #3	$37.29	13.430%	$42.298	$42.30	$42.30	$42.30
Purchase #4	$161.36	13.527%	$183.1872	$183.19	$183.20	$183.20
Purchase #5	$94.26	6.208%	$100.1117	$100.11	$100.10	$100.10
Purchase #6	$155.74	8.319%	$168.696	$168.70	$168.70	$168.70
Purchase #7	$155.56	11.784%	$173.8912	$173.89	$173.90	$173.90
7 purchase totals =	$854.22		$944.5682	$944.58	$944.60	$944.60