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	$13.85	6.813%	$14.7936	$14.79	$14.80	$14.80
Purchase #2	$134.71	13.188%	$152.4756	$152.48	$152.50	$152.50
Purchase #3	$150.79	5.252%	$158.7095	$158.71	$158.70	$158.70
Purchase #4	$25.85	5.467%	$27.2632	$27.26	$27.25	$27.30
Purchase #5	$203.36	12.854%	$229.4999	$229.50	$229.50	$229.50
Purchase #6	$38.28	11.166%	$42.5543	$42.55	$42.55	$42.60
Purchase #7	$173.81	4.864%	$182.2641	$182.26	$182.25	$182.30
7 purchase totals =	$740.65		$807.5602	$807.55	$807.55	$807.70