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	$37.52	10.149%	$41.3279	$41.33	$41.35	$41.30
Purchase #2	$185.81	7.377%	$199.5172	$199.52	$199.50	$199.50
Purchase #3	$90.59	8.687%	$98.4596	$98.46	$98.45	$98.50
Purchase #4	$54.63	7.301%	$58.6185	$58.62	$58.60	$58.60
Purchase #5	$221.87	10.172%	$244.4386	$244.44	$244.45	$244.40
Purchase #6	$136.27	11.729%	$152.2531	$152.25	$152.25	$152.30
Purchase #7	$183.86	6.756%	$196.2816	$196.28	$196.30	$196.30
7 purchase totals =	$910.55		$990.8965	$990.90	$990.90	$990.90