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	$233.30	8.404%	$252.9065	$252.91	$252.90	$252.90
Purchase #2	$122.28	7.851%	$131.8802	$131.88	$131.90	$131.90
Purchase #3	$83.25	8.781%	$90.5602	$90.56	$90.55	$90.60
Purchase #4	$77.85	6.830%	$83.1672	$83.17	$83.15	$83.20
Purchase #5	$14.50	3.228%	$14.9681	$14.97	$14.95	$15.00
Purchase #6	$247.53	4.425%	$258.4832	$258.48	$258.50	$258.50
Purchase #7	$136.84	6.557%	$145.8126	$145.81	$145.80	$145.80
7 purchase totals =	$915.55		$977.7780	$977.78	$977.75	$977.90