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	$28.40	10.155%	$31.284	$31.28	$31.30	$31.30
Purchase #2	$155.98	3.725%	$161.7903	$161.79	$161.80	$161.80
Purchase #3	$32.60	3.269%	$33.6657	$33.67	$33.65	$33.70
Purchase #4	$144.57	3.843%	$150.1258	$150.13	$150.15	$150.10
Purchase #5	$89.89	3.285%	$92.8429	$92.84	$92.85	$92.80
Purchase #6	$43.47	13.397%	$49.2937	$49.29	$49.30	$49.30
Purchase #7	$248.52	13.265%	$281.4862	$281.49	$281.50	$281.50
7 purchase totals =	$743.43		$800.4886	$800.49	$800.55	$800.50