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	$28.67	13.527%	$32.5482	$32.55	$32.55	$32.50
Purchase #2	$39.34	8.313%	$42.6103	$42.61	$42.60	$42.60
Purchase #3	$245.92	11.117%	$273.2589	$273.26	$273.25	$273.30
Purchase #4	$7.95	3.334%	$8.2151	$8.22	$8.20	$8.20
Purchase #5	$10.52	10.556%	$11.6305	$11.63	$11.65	$11.60
Purchase #6	$32.26	4.192%	$33.6123	$33.61	$33.60	$33.60
Purchase #7	$173.31	13.356%	$196.4573	$196.46	$196.45	$196.50
7 purchase totals =	$537.97		$598.3326	$598.34	$598.30	$598.30