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	$150.43	11.324%	$167.4647	$167.46	$167.45	$167.50
Purchase #2	$96.34	7.482%	$103.5482	$103.55	$103.55	$103.50
Purchase #3	$128.48	3.528%	$133.0128	$133.01	$133.00	$133.00
Purchase #4	$234.83	13.833%	$267.314	$267.31	$267.30	$267.30
Purchase #5	$155.61	5.391%	$163.9989	$164.00	$164.00	$164.00
Purchase #6	$198.56	7.200%	$212.8563	$212.86	$212.85	$212.90
Purchase #7	$196.83	12.863%	$222.1482	$222.15	$222.15	$222.10
7 purchase totals =	$1,161.08		$1,270.3431	$1,270.34	$1,270.30	$1,270.30