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	$119.39	10.137%	$131.4926	$131.49	$131.50	$131.50
Purchase #2	$36.98	8.774%	$40.2246	$40.22	$40.20	$40.20
Purchase #3	$152.65	10.442%	$168.5897	$168.59	$168.60	$168.60
Purchase #4	$37.26	13.700%	$42.3646	$42.36	$42.35	$42.40
Purchase #5	$15.43	11.841%	$17.2571	$17.26	$17.25	$17.30
Purchase #6	$199.87	10.345%	$220.5466	$220.55	$220.55	$220.50
Purchase #7	$157.76	9.105%	$172.124	$172.12	$172.10	$172.10
7 purchase totals =	$719.34		$792.5992	$792.59	$792.55	$792.60