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	$29.80	6.681%	$31.7909	$31.79	$31.80	$31.80
Purchase #2	$121.83	7.777%	$131.3047	$131.30	$131.30	$131.30
Purchase #3	$196.36	10.580%	$217.1349	$217.13	$217.15	$217.10
Purchase #4	$26.76	6.600%	$28.5262	$28.53	$28.55	$28.50
Purchase #5	$93.74	8.839%	$102.0257	$102.03	$102.05	$102.00
Purchase #6	$165.56	10.231%	$182.4984	$182.50	$182.50	$182.50
Purchase #7	$63.39	13.744%	$72.1023	$72.10	$72.10	$72.10
7 purchase totals =	$697.44		$765.3831	$765.38	$765.45	$765.30