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	$76.52	3.760%	$79.3972	$79.40	$79.40	$79.40
Purchase #2	$40.95	4.760%	$42.8992	$42.90	$42.90	$42.90
Purchase #3	$171.26	5.320%	$180.371	$180.37	$180.35	$180.40
Purchase #4	$83.88	10.803%	$92.9416	$92.94	$92.95	$92.90
Purchase #5	$228.52	9.861%	$251.0544	$251.05	$251.05	$251.10
Purchase #6	$168.81	13.109%	$190.9393	$190.94	$190.95	$190.90
Purchase #7	$84.28	3.121%	$86.9104	$86.91	$86.90	$86.90
7 purchase totals =	$854.22		$924.5131	$924.51	$924.50	$924.50