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	$94.29	5.474%	$99.4514	$99.45	$99.45	$99.50
Purchase #2	$128.78	6.601%	$137.2808	$137.28	$137.30	$137.30
Purchase #3	$203.67	7.815%	$219.5868	$219.59	$219.60	$219.60
Purchase #4	$109.53	7.680%	$117.9419	$117.94	$117.95	$117.90
Purchase #5	$87.42	3.840%	$90.7769	$90.78	$90.80	$90.80
Purchase #6	$78.76	13.671%	$89.5273	$89.53	$89.55	$89.50
Purchase #7	$178.41	3.503%	$184.6597	$184.66	$184.65	$184.70
7 purchase totals =	$880.86		$939.2248	$939.23	$939.30	$939.30