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	$181.99	5.729%	$192.4162	$192.42	$192.40	$192.40
Purchase #2	$160.56	11.244%	$178.6134	$178.61	$178.60	$178.60
Purchase #3	$92.94	9.519%	$101.787	$101.79	$101.80	$101.80
Purchase #4	$54.40	13.482%	$61.7342	$61.73	$61.75	$61.70
Purchase #5	$147.61	3.493%	$152.766	$152.77	$152.75	$152.80
Purchase #6	$63.82	13.427%	$72.3891	$72.39	$72.40	$72.40
Purchase #7	$25.50	13.321%	$28.8969	$28.90	$28.90	$28.90
7 purchase totals =	$726.82		$788.6028	$788.61	$788.60	$788.60