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	$73.62	13.466%	$83.5337	$83.53	$83.55	$83.50
Purchase #2	$76.83	8.814%	$83.6018	$83.60	$83.60	$83.60
Purchase #3	$50.29	7.583%	$54.1035	$54.10	$54.10	$54.10
Purchase #4	$102.98	12.784%	$116.145	$116.15	$116.15	$116.10
Purchase #5	$94.53	3.130%	$97.4888	$97.49	$97.50	$97.50
Purchase #6	$133.83	5.585%	$141.3044	$141.30	$141.30	$141.30
Purchase #7	$242.48	7.480%	$260.6175	$260.62	$260.60	$260.60
7 purchase totals =	$774.56		$836.7947	$836.79	$836.80	$836.70