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	$39.79	3.758%	$41.2853	$41.29	$41.30	$41.30
Purchase #2	$164.89	8.216%	$178.4374	$178.44	$178.45	$178.40
Purchase #3	$105.50	3.778%	$109.4858	$109.49	$109.50	$109.50
Purchase #4	$143.42	12.559%	$161.4321	$161.43	$161.45	$161.40
Purchase #5	$226.27	8.646%	$245.8333	$245.83	$245.85	$245.80
Purchase #6	$7.45	6.349%	$7.923	$7.92	$7.90	$7.90
Purchase #7	$86.90	5.550%	$91.723	$91.72	$91.70	$91.70
7 purchase totals =	$774.22		$836.1199	$836.12	$836.15	$836.00