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	$7.63	3.511%	$7.8979	$7.90	$7.90	$7.90
Purchase #2	$38.27	11.700%	$42.7476	$42.75	$42.75	$42.70
Purchase #3	$154.43	9.259%	$168.7287	$168.73	$168.75	$168.70
Purchase #4	$99.78	5.657%	$105.4246	$105.42	$105.40	$105.40
Purchase #5	$35.59	5.870%	$37.6791	$37.68	$37.70	$37.70
Purchase #6	$52.32	4.722%	$54.7906	$54.79	$54.80	$54.80
Purchase #7	$195.89	11.660%	$218.7308	$218.73	$218.75	$218.70
7 purchase totals =	$583.91		$635.9993	$636.00	$636.05	$635.90