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	$205.98	8.525%	$223.5398	$223.54	$223.55	$223.50
Purchase #2	$46.30	13.340%	$52.4764	$52.48	$52.50	$52.50
Purchase #3	$196.76	13.425%	$223.175	$223.18	$223.20	$223.20
Purchase #4	$133.96	4.596%	$140.1168	$140.12	$140.10	$140.10
Purchase #5	$242.45	9.261%	$264.9033	$264.90	$264.90	$264.90
Purchase #6	$40.79	6.394%	$43.3981	$43.40	$43.40	$43.40
Purchase #7	$118.56	10.644%	$131.1795	$131.18	$131.20	$131.20
7 purchase totals =	$984.80		$1,078.7889	$1,078.80	$1,078.85	$1,078.80