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	$74.44	5.206%	$78.3153	$78.32	$78.30	$78.30
Purchase #2	$51.59	4.813%	$54.073	$54.07	$54.05	$54.10
Purchase #3	$85.92	6.815%	$91.7754	$91.78	$91.80	$91.80
Purchase #4	$44.58	13.463%	$50.5818	$50.58	$50.60	$50.60
Purchase #5	$244.56	12.382%	$274.8414	$274.84	$274.85	$274.80
Purchase #6	$215.98	9.833%	$237.2173	$237.22	$237.20	$237.20
Purchase #7	$97.26	12.611%	$109.5255	$109.53	$109.55	$109.50
7 purchase totals =	$814.33		$896.3297	$896.34	$896.35	$896.30