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	$138.49	3.528%	$143.3759	$143.38	$143.40	$143.40
Purchase #2	$172.73	7.651%	$185.9456	$185.95	$185.95	$185.90
Purchase #3	$114.40	8.259%	$123.8483	$123.85	$123.85	$123.80
Purchase #4	$84.88	8.872%	$92.4106	$92.41	$92.40	$92.40
Purchase #5	$59.86	9.397%	$65.485	$65.49	$65.50	$65.50
Purchase #6	$44.89	9.849%	$49.3112	$49.31	$49.30	$49.30
Purchase #7	$89.43	11.289%	$99.5258	$99.53	$99.55	$99.50
7 purchase totals =	$704.68		$759.9024	$759.92	$759.95	$759.80