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	$249.78	8.494%	$270.9963	$271.00	$271.00	$271.00
Purchase #2	$96.37	11.797%	$107.7388	$107.74	$107.75	$107.70
Purchase #3	$55.32	7.112%	$59.2544	$59.25	$59.25	$59.30
Purchase #4	$81.50	12.736%	$91.8798	$91.88	$91.90	$91.90
Purchase #5	$46.79	12.664%	$52.7155	$52.72	$52.70	$52.70
Purchase #6	$209.93	8.558%	$227.8958	$227.90	$227.90	$227.90
Purchase #7	$146.79	4.582%	$153.5159	$153.52	$153.50	$153.50
7 purchase totals =	$886.48		$963.9965	$964.01	$964.00	$964.00