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	$40.64	3.443%	$42.0392	$42.04	$42.05	$42.00
Purchase #2	$115.72	10.337%	$127.682	$127.68	$127.70	$127.70
Purchase #3	$245.80	4.449%	$256.7356	$256.74	$256.75	$256.70
Purchase #4	$95.46	4.406%	$99.666	$99.67	$99.65	$99.70
Purchase #5	$222.43	10.786%	$246.4213	$246.42	$246.40	$246.40
Purchase #6	$207.70	5.432%	$218.9823	$218.98	$219.00	$219.00
Purchase #7	$83.61	6.361%	$88.9284	$88.93	$88.95	$88.90
7 purchase totals =	$1,011.36		$1,080.4548	$1,080.46	$1,080.50	$1,080.40