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	$133.77	4.442%	$139.7121	$139.71	$139.70	$139.70
Purchase #2	$243.64	6.624%	$259.7787	$259.78	$259.80	$259.80
Purchase #3	$25.95	9.520%	$28.4204	$28.42	$28.40	$28.40
Purchase #4	$160.53	12.628%	$180.8017	$180.80	$180.80	$180.80
Purchase #5	$37.34	7.146%	$40.0083	$40.01	$40.00	$40.00
Purchase #6	$112.64	8.198%	$121.8742	$121.87	$121.85	$121.90
Purchase #7	$234.77	8.751%	$255.3147	$255.31	$255.30	$255.30
7 purchase totals =	$948.64		$1,025.9101	$1,025.90	$1,025.85	$1,025.90