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	$190.72	6.591%	$203.2904	$203.29	$203.30	$203.30
Purchase #2	$99.47	3.387%	$102.839	$102.84	$102.85	$102.80
Purchase #3	$190.77	7.747%	$205.549	$205.55	$205.55	$205.50
Purchase #4	$47.59	12.589%	$53.5811	$53.58	$53.60	$53.60
Purchase #5	$89.36	12.601%	$100.6203	$100.62	$100.60	$100.60
Purchase #6	$88.29	5.680%	$93.3049	$93.30	$93.30	$93.30
Purchase #7	$67.89	10.380%	$74.937	$74.94	$74.95	$74.90
7 purchase totals =	$774.09		$834.1217	$834.12	$834.15	$834.00