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	$176.89	13.357%	$200.5172	$200.52	$200.50	$200.50
Purchase #2	$207.65	10.449%	$229.3473	$229.35	$229.35	$229.30
Purchase #3	$129.82	8.666%	$141.0702	$141.07	$141.05	$141.10
Purchase #4	$121.41	13.204%	$137.441	$137.44	$137.45	$137.40
Purchase #5	$38.69	10.543%	$42.7691	$42.77	$42.75	$42.80
Purchase #6	$33.66	8.432%	$36.4982	$36.50	$36.50	$36.50
Purchase #7	$81.37	11.238%	$90.5144	$90.51	$90.50	$90.50
7 purchase totals =	$789.49		$878.1574	$878.16	$878.10	$878.10