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	$89.40	13.839%	$101.7721	$101.77	$101.75	$101.80
Purchase #2	$220.64	3.294%	$227.9079	$227.91	$227.90	$227.90
Purchase #3	$176.47	8.120%	$190.7994	$190.80	$190.80	$190.80
Purchase #4	$27.76	13.811%	$31.5939	$31.59	$31.60	$31.60
Purchase #5	$84.30	7.797%	$90.8729	$90.87	$90.85	$90.90
Purchase #6	$91.38	5.655%	$96.5475	$96.55	$96.55	$96.50
Purchase #7	$239.46	8.243%	$259.1987	$259.20	$259.20	$259.20
7 purchase totals =	$929.41		$998.6924	$998.69	$998.65	$998.70