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	$159.97	7.108%	$171.3407	$171.34	$171.35	$171.30
Purchase #2	$95.52	3.411%	$98.7782	$98.78	$98.80	$98.80
Purchase #3	$214.50	7.767%	$231.1602	$231.16	$231.15	$231.20
Purchase #4	$235.41	5.482%	$248.3152	$248.32	$248.30	$248.30
Purchase #5	$51.37	8.222%	$55.5936	$55.59	$55.60	$55.60
Purchase #6	$201.49	13.300%	$228.2882	$228.29	$228.30	$228.30
Purchase #7	$207.78	7.486%	$223.3344	$223.33	$223.35	$223.30
7 purchase totals =	$1,166.04		$1,256.8105	$1,256.81	$1,256.85	$1,256.80