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	$38.34	3.762%	$39.7824	$39.78	$39.80	$39.80
Purchase #2	$122.46	9.176%	$133.6969	$133.70	$133.70	$133.70
Purchase #3	$245.38	11.447%	$273.4686	$273.47	$273.45	$273.50
Purchase #4	$37.76	11.765%	$42.2025	$42.20	$42.20	$42.20
Purchase #5	$137.80	7.638%	$148.3252	$148.33	$148.35	$148.30
Purchase #6	$78.65	4.613%	$82.2781	$82.28	$82.30	$82.30
Purchase #7	$138.81	9.742%	$152.3329	$152.33	$152.35	$152.30
7 purchase totals =	$799.20		$872.0866	$872.09	$872.15	$872.10