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	$217.43	11.547%	$242.5366	$242.54	$242.55	$242.50
Purchase #2	$35.76	4.755%	$37.4604	$37.46	$37.45	$37.50
Purchase #3	$208.50	13.831%	$237.3376	$237.34	$237.35	$237.30
Purchase #4	$30.67	8.567%	$33.2975	$33.30	$33.30	$33.30
Purchase #5	$31.73	6.175%	$33.6893	$33.69	$33.70	$33.70
Purchase #6	$128.73	7.816%	$138.7915	$138.79	$138.80	$138.80
Purchase #7	$213.61	5.693%	$225.7708	$225.77	$225.75	$225.80
7 purchase totals =	$866.43		$948.8837	$948.89	$948.90	$948.90