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	$238.25	12.112%	$267.1068	$267.11	$267.10	$267.10
Purchase #2	$191.94	12.733%	$216.3797	$216.38	$216.40	$216.40
Purchase #3	$89.83	9.405%	$98.2785	$98.28	$98.30	$98.30
Purchase #4	$123.88	6.377%	$131.7798	$131.78	$131.80	$131.80
Purchase #5	$111.92	9.702%	$122.7785	$122.78	$122.80	$122.80
Purchase #6	$39.66	9.870%	$43.5744	$43.57	$43.55	$43.60
Purchase #7	$117.30	7.830%	$126.4846	$126.48	$126.50	$126.50
7 purchase totals =	$912.78		$1,006.3823	$1,006.38	$1,006.45	$1,006.50