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	$161.42	4.217%	$168.2271	$168.23	$168.25	$168.20
Purchase #2	$173.92	4.707%	$182.1064	$182.11	$182.10	$182.10
Purchase #3	$69.32	13.859%	$78.9271	$78.93	$78.95	$78.90
Purchase #4	$83.99	9.484%	$91.9556	$91.96	$91.95	$92.00
Purchase #5	$7.26	3.394%	$7.5064	$7.51	$7.50	$7.50
Purchase #6	$237.47	5.662%	$250.9156	$250.92	$250.90	$250.90
Purchase #7	$141.55	5.215%	$148.9318	$148.93	$148.95	$148.90
7 purchase totals =	$874.93		$928.5700	$928.59	$928.60	$928.50