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	$67.81	6.497%	$72.2156	$72.22	$72.20	$72.20
Purchase #2	$121.89	5.701%	$128.8389	$128.84	$128.85	$128.80
Purchase #3	$83.49	8.343%	$90.4556	$90.46	$90.45	$90.50
Purchase #4	$14.43	13.160%	$16.329	$16.33	$16.35	$16.30
Purchase #5	$57.38	13.225%	$64.9685	$64.97	$64.95	$65.00
Purchase #6	$23.39	10.272%	$25.7926	$25.79	$25.80	$25.80
Purchase #7	$115.46	11.655%	$128.9169	$128.92	$128.90	$128.90
7 purchase totals =	$483.85		$527.5171	$527.53	$527.50	$527.50