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	$98.80	4.138%	$102.8883	$102.89	$102.90	$102.90
Purchase #2	$180.94	8.362%	$196.0702	$196.07	$196.05	$196.10
Purchase #3	$172.72	11.169%	$192.0111	$192.01	$192.00	$192.00
Purchase #4	$233.99	12.324%	$262.8269	$262.83	$262.85	$262.80
Purchase #5	$44.64	6.557%	$47.567	$47.57	$47.55	$47.60
Purchase #6	$100.95	10.558%	$111.6083	$111.61	$111.60	$111.60
Purchase #7	$218.40	11.664%	$243.8742	$243.87	$243.85	$243.90
7 purchase totals =	$1,050.44		$1,156.8460	$1,156.85	$1,156.80	$1,156.90