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	$154.38	10.278%	$170.2472	$170.25	$170.25	$170.20
Purchase #2	$169.38	9.220%	$184.9968	$185.00	$185.00	$185.00
Purchase #3	$32.81	13.722%	$37.3122	$37.31	$37.30	$37.30
Purchase #4	$250.75	12.117%	$281.1334	$281.13	$281.15	$281.10
Purchase #5	$6.48	13.423%	$7.3498	$7.35	$7.35	$7.30
Purchase #6	$18.96	6.148%	$20.1257	$20.13	$20.15	$20.10
Purchase #7	$212.30	7.165%	$227.5113	$227.51	$227.50	$227.50
7 purchase totals =	$845.06		$928.6764	$928.68	$928.70	$928.50