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	$80.89	11.520%	$90.2085	$90.21	$90.20	$90.20
Purchase #2	$154.29	8.767%	$167.8166	$167.82	$167.80	$167.80
Purchase #3	$224.34	7.387%	$240.912	$240.91	$240.90	$240.90
Purchase #4	$207.73	11.352%	$231.3115	$231.31	$231.30	$231.30
Purchase #5	$213.76	7.188%	$229.1251	$229.13	$229.15	$229.10
Purchase #6	$136.65	11.818%	$152.7993	$152.80	$152.80	$152.80
Purchase #7	$83.74	8.178%	$90.5883	$90.59	$90.60	$90.60
7 purchase totals =	$1,101.40		$1,202.7613	$1,202.77	$1,202.75	$1,202.70