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	$42.57	8.744%	$46.2923	$46.29	$46.30	$46.30
Purchase #2	$235.76	12.213%	$264.5534	$264.55	$264.55	$264.60
Purchase #3	$21.87	8.302%	$23.6856	$23.69	$23.70	$23.70
Purchase #4	$182.38	12.664%	$205.4766	$205.48	$205.50	$205.50
Purchase #5	$25.84	4.150%	$26.9124	$26.91	$26.90	$26.90
Purchase #6	$51.40	11.536%	$57.3295	$57.33	$57.35	$57.30
Purchase #7	$41.76	4.270%	$43.5432	$43.54	$43.55	$43.50
7 purchase totals =	$601.58		$667.7930	$667.79	$667.85	$667.80