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	$92.40	13.498%	$104.8722	$104.87	$104.85	$104.90
Purchase #2	$209.48	9.611%	$229.6131	$229.61	$229.60	$229.60
Purchase #3	$118.51	3.622%	$122.8024	$122.80	$122.80	$122.80
Purchase #4	$60.39	8.631%	$65.6023	$65.60	$65.60	$65.60
Purchase #5	$200.33	9.780%	$219.9223	$219.92	$219.90	$219.90
Purchase #6	$41.61	3.833%	$43.2049	$43.20	$43.20	$43.20
Purchase #7	$35.72	13.575%	$40.569	$40.57	$40.55	$40.60
7 purchase totals =	$758.44		$826.5862	$826.57	$826.50	$826.60