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	$7.54	13.322%	$8.5445	$8.54	$8.55	$8.50
Purchase #2	$74.37	9.116%	$81.1496	$81.15	$81.15	$81.10
Purchase #3	$188.72	4.201%	$196.6481	$196.65	$196.65	$196.60
Purchase #4	$20.52	9.620%	$22.494	$22.49	$22.50	$22.50
Purchase #5	$239.63	13.756%	$272.5935	$272.59	$272.60	$272.60
Purchase #6	$219.73	11.445%	$244.8781	$244.88	$244.90	$244.90
Purchase #7	$82.35	4.766%	$86.2748	$86.27	$86.25	$86.30
7 purchase totals =	$832.86		$912.5826	$912.57	$912.60	$912.50