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	$204.72	12.265%	$229.8289	$229.83	$229.85	$229.80
Purchase #2	$6.34	12.346%	$7.1227	$7.12	$7.10	$7.10
Purchase #3	$88.37	9.464%	$96.7333	$96.73	$96.75	$96.70
Purchase #4	$150.72	13.868%	$171.6218	$171.62	$171.60	$171.60
Purchase #5	$6.60	10.167%	$7.271	$7.27	$7.25	$7.30
Purchase #6	$24.89	10.528%	$27.5104	$27.51	$27.50	$27.50
Purchase #7	$66.70	5.524%	$70.3845	$70.38	$70.40	$70.40
7 purchase totals =	$548.34		$610.4726	$610.46	$610.45	$610.40