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	$25.91	10.386%	$28.601	$28.60	$28.60	$28.60
Purchase #2	$71.33	8.704%	$77.5386	$77.54	$77.55	$77.50
Purchase #3	$150.94	11.547%	$168.369	$168.37	$168.35	$168.40
Purchase #4	$37.99	12.639%	$42.7916	$42.79	$42.80	$42.80
Purchase #5	$244.59	11.165%	$271.8985	$271.90	$271.90	$271.90
Purchase #6	$90.61	9.821%	$99.5088	$99.51	$99.50	$99.50
Purchase #7	$99.99	11.493%	$111.4819	$111.48	$111.50	$111.50
7 purchase totals =	$721.36		$800.1894	$800.19	$800.20	$800.20