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	$81.47	9.714%	$89.384	$89.38	$89.40	$89.40
Purchase #2	$245.46	5.630%	$259.2794	$259.28	$259.30	$259.30
Purchase #3	$186.48	12.361%	$209.5308	$209.53	$209.55	$209.50
Purchase #4	$161.38	3.622%	$167.2252	$167.23	$167.25	$167.20
Purchase #5	$51.86	9.663%	$56.8712	$56.87	$56.85	$56.90
Purchase #6	$136.27	8.228%	$147.4823	$147.48	$147.50	$147.50
Purchase #7	$36.99	8.657%	$40.1922	$40.19	$40.20	$40.20
7 purchase totals =	$899.91		$969.9651	$969.96	$970.05	$970.00