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	$79.98	12.238%	$89.768	$89.77	$89.75	$89.80
Purchase #2	$35.81	11.768%	$40.0241	$40.02	$40.00	$40.00
Purchase #3	$235.98	6.672%	$251.7246	$251.72	$251.70	$251.70
Purchase #4	$172.68	6.507%	$183.9163	$183.92	$183.90	$183.90
Purchase #5	$171.65	10.702%	$190.02	$190.02	$190.00	$190.00
Purchase #6	$59.85	4.486%	$62.5349	$62.53	$62.55	$62.50
Purchase #7	$181.40	9.699%	$198.994	$198.99	$199.00	$199.00
7 purchase totals =	$937.35		$1,016.9819	$1,016.97	$1,016.90	$1,016.90