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	$54.89	5.328%	$57.8145	$57.81	$57.80	$57.80
Purchase #2	$137.90	8.663%	$149.8463	$149.85	$149.85	$149.80
Purchase #3	$156.63	5.181%	$164.745	$164.75	$164.75	$164.70
Purchase #4	$219.59	13.602%	$249.4586	$249.46	$249.45	$249.50
Purchase #5	$125.34	12.812%	$141.3986	$141.40	$141.40	$141.40
Purchase #6	$87.29	13.874%	$99.4006	$99.40	$99.40	$99.40
Purchase #7	$227.81	8.447%	$247.0531	$247.05	$247.05	$247.10
7 purchase totals =	$1,009.45		$1,109.7167	$1,109.72	$1,109.70	$1,109.70