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	$122.98	3.480%	$127.2597	$127.26	$127.25	$127.30
Purchase #2	$38.61	6.537%	$41.1339	$41.13	$41.15	$41.10
Purchase #3	$129.29	7.872%	$139.4677	$139.47	$139.45	$139.50
Purchase #4	$129.98	8.459%	$140.975	$140.98	$141.00	$141.00
Purchase #5	$138.69	13.526%	$157.4492	$157.45	$157.45	$157.40
Purchase #6	$32.44	3.460%	$33.5624	$33.56	$33.55	$33.60
Purchase #7	$23.84	13.789%	$27.1273	$27.13	$27.15	$27.10
7 purchase totals =	$615.83		$666.9752	$666.98	$667.00	$667.00