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	$63.56	5.410%	$66.9986	$67.00	$67.00	$67.00
Purchase #2	$89.42	12.375%	$100.4857	$100.49	$100.50	$100.50
Purchase #3	$60.77	5.748%	$64.2631	$64.26	$64.25	$64.30
Purchase #4	$171.57	6.647%	$182.9743	$182.97	$182.95	$183.00
Purchase #5	$30.70	8.310%	$33.2512	$33.25	$33.25	$33.30
Purchase #6	$247.92	4.816%	$259.8598	$259.86	$259.85	$259.90
Purchase #7	$196.85	13.527%	$223.4779	$223.48	$223.50	$223.50
7 purchase totals =	$860.79		$931.3106	$931.31	$931.30	$931.50