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	$118.89	3.717%	$123.3091	$123.31	$123.30	$123.30
Purchase #2	$164.52	4.599%	$172.0863	$172.09	$172.10	$172.10
Purchase #3	$35.46	7.272%	$38.0387	$38.04	$38.05	$38.00
Purchase #4	$34.52	10.154%	$38.0252	$38.03	$38.05	$38.00
Purchase #5	$206.61	7.689%	$222.4962	$222.50	$222.50	$222.50
Purchase #6	$165.62	10.797%	$183.502	$183.50	$183.50	$183.50
Purchase #7	$33.34	11.850%	$37.2908	$37.29	$37.30	$37.30
7 purchase totals =	$758.96		$814.7483	$814.76	$814.80	$814.70