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	$74.27	5.524%	$78.3727	$78.37	$78.35	$78.40
Purchase #2	$227.54	7.431%	$244.4485	$244.45	$244.45	$244.40
Purchase #3	$113.89	13.168%	$128.887	$128.89	$128.90	$128.90
Purchase #4	$18.53	13.481%	$21.028	$21.03	$21.05	$21.00
Purchase #5	$186.81	3.756%	$193.8266	$193.83	$193.85	$193.80
Purchase #6	$121.83	7.275%	$130.6931	$130.69	$130.70	$130.70
Purchase #7	$162.53	10.431%	$179.4835	$179.48	$179.50	$179.50
7 purchase totals =	$905.40		$976.7394	$976.74	$976.80	$976.70