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	$100.73	8.341%	$109.1319	$109.13	$109.15	$109.10
Purchase #2	$171.46	8.761%	$186.4816	$186.48	$186.50	$186.50
Purchase #3	$217.40	7.196%	$233.0441	$233.04	$233.05	$233.00
Purchase #4	$186.41	10.807%	$206.5553	$206.56	$206.55	$206.60
Purchase #5	$153.82	11.550%	$171.5862	$171.59	$171.60	$171.60
Purchase #6	$101.94	10.545%	$112.6896	$112.69	$112.70	$112.70
Purchase #7	$66.97	3.630%	$69.401	$69.40	$69.40	$69.40
7 purchase totals =	$998.73		$1,088.8897	$1,088.89	$1,088.95	$1,088.90