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	$180.73	4.273%	$188.4526	$188.45	$188.45	$188.50
Purchase #2	$213.78	3.156%	$220.5269	$220.53	$220.55	$220.50
Purchase #3	$124.36	12.418%	$139.803	$139.80	$139.80	$139.80
Purchase #4	$87.83	12.125%	$98.4794	$98.48	$98.50	$98.50
Purchase #5	$171.50	10.465%	$189.4475	$189.45	$189.45	$189.40
Purchase #6	$77.28	7.589%	$83.1448	$83.14	$83.15	$83.10
Purchase #7	$95.96	4.342%	$100.1266	$100.13	$100.15	$100.10
7 purchase totals =	$951.44		$1,019.9808	$1,019.98	$1,020.05	$1,019.90