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	$85.73	6.625%	$91.4096	$91.41	$91.40	$91.40
Purchase #2	$227.79	13.400%	$258.3139	$258.31	$258.30	$258.30
Purchase #3	$82.61	8.833%	$89.9069	$89.91	$89.90	$89.90
Purchase #4	$173.98	7.179%	$186.47	$186.47	$186.45	$186.50
Purchase #5	$250.72	9.425%	$274.3504	$274.35	$274.35	$274.40
Purchase #6	$242.75	7.697%	$261.4345	$261.43	$261.45	$261.40
Purchase #7	$60.40	10.272%	$66.6043	$66.60	$66.60	$66.60
7 purchase totals =	$1,123.98		$1,228.4896	$1,228.48	$1,228.45	$1,228.50