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	$41.98	3.598%	$43.4904	$43.49	$43.50	$43.50
Purchase #2	$240.52	10.131%	$264.8871	$264.89	$264.90	$264.90
Purchase #3	$52.35	4.746%	$54.8345	$54.83	$54.85	$54.80
Purchase #4	$221.25	11.819%	$247.3995	$247.40	$247.40	$247.40
Purchase #5	$37.44	7.332%	$40.1851	$40.19	$40.20	$40.20
Purchase #6	$63.49	11.494%	$70.7875	$70.79	$70.80	$70.80
Purchase #7	$100.48	8.503%	$109.0238	$109.02	$109.00	$109.00
7 purchase totals =	$757.51		$830.6079	$830.61	$830.65	$830.60