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	$217.66	11.819%	$243.3852	$243.39	$243.40	$243.40
Purchase #2	$246.94	10.686%	$273.328	$273.33	$273.35	$273.30
Purchase #3	$85.83	4.207%	$89.4409	$89.44	$89.45	$89.40
Purchase #4	$132.91	10.357%	$146.6755	$146.68	$146.70	$146.70
Purchase #5	$37.32	10.664%	$41.2998	$41.30	$41.30	$41.30
Purchase #6	$86.57	11.639%	$96.6459	$96.65	$96.65	$96.60
Purchase #7	$6.90	8.226%	$7.4676	$7.47	$7.45	$7.50
7 purchase totals =	$814.13		$898.2429	$898.26	$898.30	$898.20