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	$242.72	12.334%	$272.6571	$272.66	$272.65	$272.70
Purchase #2	$199.54	8.160%	$215.8225	$215.82	$215.80	$215.80
Purchase #3	$32.80	7.538%	$35.2725	$35.27	$35.25	$35.30
Purchase #4	$215.40	4.655%	$225.4269	$225.43	$225.45	$225.40
Purchase #5	$81.66	5.110%	$85.8328	$85.83	$85.85	$85.80
Purchase #6	$163.79	4.580%	$171.2916	$171.29	$171.30	$171.30
Purchase #7	$98.25	6.870%	$104.9998	$105.00	$105.00	$105.00
7 purchase totals =	$1,034.16		$1,111.3032	$1,111.30	$1,111.30	$1,111.30