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	$7.92	7.867%	$8.5431	$8.54	$8.55	$8.50
Purchase #2	$9.86	13.679%	$11.2087	$11.21	$11.20	$11.20
Purchase #3	$250.62	12.717%	$282.4913	$282.49	$282.50	$282.50
Purchase #4	$137.41	3.160%	$141.7522	$141.75	$141.75	$141.80
Purchase #5	$196.44	13.764%	$223.478	$223.48	$223.50	$223.50
Purchase #6	$139.36	8.106%	$150.6565	$150.66	$150.65	$150.70
Purchase #7	$82.67	9.544%	$90.56	$90.56	$90.55	$90.60
7 purchase totals =	$824.28		$908.6898	$908.69	$908.70	$908.80