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	$76.98	4.549%	$80.4818	$80.48	$80.50	$80.50
Purchase #2	$136.58	12.374%	$153.4804	$153.48	$153.50	$153.50
Purchase #3	$250.30	8.602%	$271.8308	$271.83	$271.85	$271.80
Purchase #4	$9.82	8.588%	$10.6633	$10.66	$10.65	$10.70
Purchase #5	$216.48	13.270%	$245.2069	$245.21	$245.20	$245.20
Purchase #6	$171.88	8.141%	$185.8728	$185.87	$185.85	$185.90
Purchase #7	$83.51	7.557%	$89.8209	$89.82	$89.80	$89.80
7 purchase totals =	$945.55		$1,037.3569	$1,037.35	$1,037.35	$1,037.40