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	$17.73	10.496%	$19.5909	$19.59	$19.60	$19.60
Purchase #2	$83.35	8.637%	$90.5489	$90.55	$90.55	$90.50
Purchase #3	$7.34	7.228%	$7.8705	$7.87	$7.85	$7.90
Purchase #4	$231.73	9.724%	$254.2634	$254.26	$254.25	$254.30
Purchase #5	$140.98	8.503%	$152.9675	$152.97	$152.95	$153.00
Purchase #6	$115.79	3.518%	$119.8635	$119.86	$119.85	$119.90
Purchase #7	$100.81	7.860%	$108.7337	$108.73	$108.75	$108.70
7 purchase totals =	$697.73		$753.8384	$753.83	$753.80	$753.90