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	$234.94	3.262%	$242.6037	$242.60	$242.60	$242.60
Purchase #2	$161.60	5.165%	$169.9466	$169.95	$169.95	$169.90
Purchase #3	$122.79	3.801%	$127.4572	$127.46	$127.45	$127.50
Purchase #4	$16.92	9.231%	$18.4819	$18.48	$18.50	$18.50
Purchase #5	$59.59	9.750%	$65.4	$65.40	$65.40	$65.40
Purchase #6	$76.31	12.467%	$85.8236	$85.82	$85.80	$85.80
Purchase #7	$209.98	4.346%	$219.1057	$219.11	$219.10	$219.10
7 purchase totals =	$882.13		$928.8187	$928.82	$928.80	$928.80