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	$55.86	6.861%	$59.6926	$59.69	$59.70	$59.70
Purchase #2	$87.47	3.112%	$90.1921	$90.19	$90.20	$90.20
Purchase #3	$112.79	11.364%	$125.6075	$125.61	$125.60	$125.60
Purchase #4	$202.53	8.139%	$219.0139	$219.01	$219.00	$219.00
Purchase #5	$13.44	5.386%	$14.1639	$14.16	$14.15	$14.20
Purchase #6	$130.46	8.455%	$141.4904	$141.49	$141.50	$141.50
Purchase #7	$138.90	10.375%	$153.3109	$153.31	$153.30	$153.30
7 purchase totals =	$741.45		$803.4713	$803.46	$803.45	$803.50