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	$75.69	3.818%	$78.5798	$78.58	$78.60	$78.60
Purchase #2	$232.32	13.138%	$262.8422	$262.84	$262.85	$262.80
Purchase #3	$236.59	10.439%	$261.2876	$261.29	$261.30	$261.30
Purchase #4	$35.59	11.304%	$39.6131	$39.61	$39.60	$39.60
Purchase #5	$48.87	11.632%	$54.5546	$54.55	$54.55	$54.60
Purchase #6	$211.75	5.700%	$223.8198	$223.82	$223.80	$223.80
Purchase #7	$26.25	8.618%	$28.5122	$28.51	$28.50	$28.50
7 purchase totals =	$867.06		$949.2093	$949.20	$949.20	$949.20