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	$69.51	12.460%	$78.1709	$78.17	$78.15	$78.20
Purchase #2	$87.96	4.629%	$92.0317	$92.03	$92.05	$92.00
Purchase #3	$19.97	9.781%	$21.9233	$21.92	$21.90	$21.90
Purchase #4	$42.39	10.182%	$46.7061	$46.71	$46.70	$46.70
Purchase #5	$212.54	9.830%	$233.4327	$233.43	$233.45	$233.40
Purchase #6	$133.56	11.759%	$149.2653	$149.27	$149.25	$149.30
Purchase #7	$189.64	10.700%	$209.9315	$209.93	$209.95	$209.90
7 purchase totals =	$755.57		$831.4615	$831.46	$831.45	$831.40