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	$106.85	9.759%	$117.2775	$117.28	$117.30	$117.30
Purchase #2	$105.89	6.187%	$112.4414	$112.44	$112.45	$112.40
Purchase #3	$35.79	8.234%	$38.7369	$38.74	$38.75	$38.70
Purchase #4	$145.27	3.788%	$150.7728	$150.77	$150.75	$150.80
Purchase #5	$138.88	6.280%	$147.6017	$147.60	$147.60	$147.60
Purchase #6	$76.64	8.125%	$82.867	$82.87	$82.85	$82.90
Purchase #7	$128.41	9.217%	$140.2455	$140.25	$140.25	$140.20
7 purchase totals =	$737.73		$789.9428	$789.95	$789.95	$789.90