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	$35.41	13.482%	$40.184	$40.18	$40.20	$40.20
Purchase #2	$89.58	7.314%	$96.1319	$96.13	$96.15	$96.10
Purchase #3	$59.29	10.526%	$65.5309	$65.53	$65.55	$65.50
Purchase #4	$18.74	8.464%	$20.3262	$20.33	$20.35	$20.30
Purchase #5	$222.40	11.336%	$247.6113	$247.61	$247.60	$247.60
Purchase #6	$194.60	7.560%	$209.3118	$209.31	$209.30	$209.30
Purchase #7	$136.61	10.449%	$150.8844	$150.88	$150.90	$150.90
7 purchase totals =	$756.63		$829.9805	$829.97	$830.05	$829.90