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	$90.41	8.267%	$97.8842	$97.88	$97.90	$97.90
Purchase #2	$248.32	8.467%	$269.3453	$269.35	$269.35	$269.30
Purchase #3	$76.41	11.352%	$85.0841	$85.08	$85.10	$85.10
Purchase #4	$95.92	7.557%	$103.1687	$103.17	$103.15	$103.20
Purchase #5	$19.30	4.686%	$20.2044	$20.20	$20.20	$20.20
Purchase #6	$99.58	12.370%	$111.898	$111.90	$111.90	$111.90
Purchase #7	$112.46	11.616%	$125.5234	$125.52	$125.50	$125.50
7 purchase totals =	$742.40		$813.1081	$813.10	$813.10	$813.10