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	$134.98	13.106%	$152.6705	$152.67	$152.65	$152.70
Purchase #2	$135.76	4.186%	$141.4429	$141.44	$141.45	$141.40
Purchase #3	$39.73	3.219%	$41.0089	$41.01	$41.00	$41.00
Purchase #4	$40.38	13.391%	$45.7873	$45.79	$45.80	$45.80
Purchase #5	$211.90	7.671%	$228.1548	$228.15	$228.15	$228.20
Purchase #6	$248.71	6.602%	$265.1298	$265.13	$265.15	$265.10
Purchase #7	$39.72	6.745%	$42.3991	$42.40	$42.40	$42.40
7 purchase totals =	$851.18		$916.5933	$916.59	$916.60	$916.60