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	$26.59	5.753%	$28.1197	$28.12	$28.10	$28.10
Purchase #2	$113.65	13.203%	$128.6552	$128.66	$128.65	$128.70
Purchase #3	$164.60	9.404%	$180.079	$180.08	$180.10	$180.10
Purchase #4	$47.51	9.105%	$51.8358	$51.84	$51.85	$51.80
Purchase #5	$160.35	13.216%	$181.5419	$181.54	$181.55	$181.50
Purchase #6	$125.90	13.602%	$143.0249	$143.02	$143.00	$143.00
Purchase #7	$182.83	7.377%	$196.3174	$196.32	$196.30	$196.30
7 purchase totals =	$821.43		$909.5739	$909.58	$909.55	$909.50