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	$40.58	3.689%	$42.077	$42.08	$42.10	$42.10
Purchase #2	$192.27	3.570%	$199.134	$199.13	$199.15	$199.10
Purchase #3	$177.84	12.401%	$199.8939	$199.89	$199.90	$199.90
Purchase #4	$217.66	3.110%	$224.4292	$224.43	$224.45	$224.40
Purchase #5	$119.78	9.736%	$131.4418	$131.44	$131.45	$131.40
Purchase #6	$64.48	9.160%	$70.3864	$70.39	$70.40	$70.40
Purchase #7	$79.37	3.198%	$81.9083	$81.91	$81.90	$81.90
7 purchase totals =	$891.98		$949.2706	$949.27	$949.35	$949.20