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	$158.69	8.493%	$172.1675	$172.17	$172.15	$172.20
Purchase #2	$169.27	13.107%	$191.4562	$191.46	$191.45	$191.50
Purchase #3	$91.32	12.344%	$102.5925	$102.59	$102.60	$102.60
Purchase #4	$56.66	11.208%	$63.0105	$63.01	$63.00	$63.00
Purchase #5	$218.99	4.636%	$229.1424	$229.14	$229.15	$229.10
Purchase #6	$140.90	4.565%	$147.3321	$147.33	$147.35	$147.30
Purchase #7	$20.70	3.483%	$21.421	$21.42	$21.40	$21.40
7 purchase totals =	$856.53		$927.1222	$927.12	$927.10	$927.10