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	$80.55	11.107%	$89.4967	$89.50	$89.50	$89.50
Purchase #2	$126.96	8.343%	$137.5523	$137.55	$137.55	$137.60
Purchase #3	$160.44	11.763%	$179.3126	$179.31	$179.30	$179.30
Purchase #4	$235.91	8.138%	$255.1084	$255.11	$255.10	$255.10
Purchase #5	$31.49	12.328%	$35.3721	$35.37	$35.35	$35.40
Purchase #6	$27.54	3.193%	$28.4194	$28.42	$28.40	$28.40
Purchase #7	$231.33	13.290%	$262.0738	$262.07	$262.05	$262.10
7 purchase totals =	$894.22		$987.3353	$987.33	$987.25	$987.40