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	$40.53	5.513%	$42.7644	$42.76	$42.75	$42.80
Purchase #2	$250.92	9.143%	$273.8616	$273.86	$273.85	$273.90
Purchase #3	$75.56	9.510%	$82.7458	$82.75	$82.75	$82.70
Purchase #4	$192.54	7.141%	$206.2893	$206.29	$206.30	$206.30
Purchase #5	$233.26	8.854%	$253.9128	$253.91	$253.90	$253.90
Purchase #6	$210.43	5.247%	$221.4713	$221.47	$221.45	$221.50
Purchase #7	$226.69	6.106%	$240.5317	$240.53	$240.55	$240.50
7 purchase totals =	$1,229.93		$1,321.5769	$1,321.57	$1,321.55	$1,321.60