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	$42.58	7.318%	$45.696	$45.70	$45.70	$45.70
Purchase #2	$231.70	11.742%	$258.9062	$258.91	$258.90	$258.90
Purchase #3	$237.78	12.117%	$266.5918	$266.59	$266.60	$266.60
Purchase #4	$37.92	6.288%	$40.3044	$40.30	$40.30	$40.30
Purchase #5	$8.33	9.491%	$9.1206	$9.12	$9.10	$9.10
Purchase #6	$160.54	5.216%	$168.9138	$168.91	$168.90	$168.90
Purchase #7	$185.88	12.375%	$208.8827	$208.88	$208.90	$208.90
7 purchase totals =	$904.73		$998.4155	$998.41	$998.40	$998.40