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	$36.63	12.696%	$41.2805	$41.28	$41.30	$41.30
Purchase #2	$129.66	3.285%	$133.9193	$133.92	$133.90	$133.90
Purchase #3	$64.77	3.792%	$67.2261	$67.23	$67.25	$67.20
Purchase #4	$167.42	12.580%	$188.4814	$188.48	$188.50	$188.50
Purchase #5	$34.66	5.460%	$36.5524	$36.55	$36.55	$36.60
Purchase #6	$116.36	9.413%	$127.313	$127.31	$127.30	$127.30
Purchase #7	$68.30	4.505%	$71.3769	$71.38	$71.40	$71.40
7 purchase totals =	$617.80		$666.1496	$666.15	$666.20	$666.20