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	$155.97	9.577%	$170.9072	$170.91	$170.90	$170.90
Purchase #2	$152.64	4.341%	$159.2661	$159.27	$159.25	$159.30
Purchase #3	$55.86	7.136%	$59.8462	$59.85	$59.85	$59.80
Purchase #4	$154.77	5.666%	$163.5393	$163.54	$163.55	$163.50
Purchase #5	$35.57	6.188%	$37.7711	$37.77	$37.75	$37.80
Purchase #6	$66.35	8.721%	$72.1364	$72.14	$72.15	$72.10
Purchase #7	$138.62	8.825%	$150.8532	$150.85	$150.85	$150.90
7 purchase totals =	$759.78		$814.3195	$814.33	$814.30	$814.30