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	$51.74	10.426%	$57.1344	$57.13	$57.15	$57.10
Purchase #2	$215.38	7.417%	$231.3547	$231.35	$231.35	$231.40
Purchase #3	$86.68	5.350%	$91.3174	$91.32	$91.30	$91.30
Purchase #4	$112.35	3.594%	$116.3879	$116.39	$116.40	$116.40
Purchase #5	$130.81	6.671%	$139.5363	$139.54	$139.55	$139.50
Purchase #6	$67.96	7.160%	$72.8259	$72.83	$72.85	$72.80
Purchase #7	$108.99	6.325%	$115.8836	$115.88	$115.90	$115.90
7 purchase totals =	$773.91		$824.4402	$824.44	$824.50	$824.40