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	$64.65	12.502%	$72.7325	$72.73	$72.75	$72.70
Purchase #2	$19.74	8.724%	$21.4621	$21.46	$21.45	$21.50
Purchase #3	$209.43	3.726%	$217.2334	$217.23	$217.25	$217.20
Purchase #4	$220.69	9.462%	$241.5717	$241.57	$241.55	$241.60
Purchase #5	$35.38	5.731%	$37.4076	$37.41	$37.40	$37.40
Purchase #6	$29.51	7.129%	$31.6138	$31.61	$31.60	$31.60
Purchase #7	$19.33	8.166%	$20.9085	$20.91	$20.90	$20.90
7 purchase totals =	$598.73		$642.9296	$642.92	$642.90	$642.90