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	$83.83	7.198%	$89.8641	$89.86	$89.85	$89.90
Purchase #2	$203.43	7.132%	$217.9386	$217.94	$217.95	$217.90
Purchase #3	$83.93	13.624%	$95.3646	$95.36	$95.35	$95.40
Purchase #4	$215.88	8.645%	$234.5428	$234.54	$234.55	$234.50
Purchase #5	$86.62	11.198%	$96.3197	$96.32	$96.30	$96.30
Purchase #6	$45.32	3.196%	$46.7684	$46.77	$46.75	$46.80
Purchase #7	$7.95	13.658%	$9.0358	$9.04	$9.05	$9.00
7 purchase totals =	$726.96		$789.8340	$789.83	$789.80	$789.80