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	$72.82	12.424%	$81.8672	$81.87	$81.85	$81.90
Purchase #2	$109.88	12.531%	$123.6491	$123.65	$123.65	$123.60
Purchase #3	$81.96	4.248%	$85.4417	$85.44	$85.45	$85.40
Purchase #4	$44.58	13.849%	$50.7539	$50.75	$50.75	$50.80
Purchase #5	$207.49	4.538%	$216.9059	$216.91	$216.90	$216.90
Purchase #6	$48.30	6.675%	$51.524	$51.52	$51.50	$51.50
Purchase #7	$63.42	8.424%	$68.7625	$68.76	$68.75	$68.80
7 purchase totals =	$628.45		$678.9043	$678.90	$678.85	$678.90