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	$7.37	7.174%	$7.8987	$7.90	$7.90	$7.90
Purchase #2	$48.86	9.284%	$53.3962	$53.40	$53.40	$53.40
Purchase #3	$159.80	3.435%	$165.2891	$165.29	$165.30	$165.30
Purchase #4	$132.29	3.206%	$136.5312	$136.53	$136.55	$136.50
Purchase #5	$209.92	13.300%	$237.8394	$237.84	$237.85	$237.80
Purchase #6	$126.73	12.846%	$143.0097	$143.01	$143.00	$143.00
Purchase #7	$172.35	7.275%	$184.8885	$184.89	$184.90	$184.90
7 purchase totals =	$857.32		$928.8528	$928.86	$928.90	$928.80